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phunix/minix/servers/vfs/select.c
David van Moolenbroek 722cbc6186 VFS: change select(2) semantics for closed filps 
If a select(2) call was issued on a file descriptor for which the file
pointer was closed due to invalidation (FILP_CLOSED), typically as the
result of a character/socket driver dying, the call would previously
return with an error: EINTR upon call entry or EIO on invalidation at
at a later time.  Especially the former could severely confuse
applications, which would assume the call was interrupted by a signal,
restart the select call and immediately get EINTR again, ad infinitum.

This patch changes the select(2) semantics such that for closed filps,
the file descriptor is returned as readable and/or writable (depending
on the requested operations), as such letting the entire select call
finish successfully.  Applications will then typically attempt to read
from and/or write to the file descriptor, resulting in an I/O error
that they should generally be better equipped to handle.

This patch also fixes a potential problem with returning early from a
select(2) call if a bad file descriptor is given: previously, in such
cases not all actions taken so far would be undone; now they are.

Change-Id: Ia6581f8789473a8a6c200852fccf552691a17025
2017-03-09 23:39:50 +00:00

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/* Implement entry point to select system call.
*
* The entry points into this file are
* do_select: perform the SELECT system call
* select_callback: notify select system of possible fd operation
* select_unsuspend_by_endpt: cancel a blocking select on exiting driver
*
* The select code uses minimal locking, so that the replies from character
* drivers can be processed without blocking. Filps are locked only for pipes.
* We make the assumption that any other structures and fields are safe to
* check (and possibly change) as long as we know that a process is blocked on
* a select(2) call, meaning that all involved filps are guaranteed to stay
* open until either we finish the select call, it the process gets interrupted
* by a signal.
*/
#include "fs.h"
#include <sys/fcntl.h>
#include <sys/time.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <minix/callnr.h>
#include <minix/u64.h>
#include <string.h>
#include <assert.h>
#include "file.h"
#include "vnode.h"
/* max. number of simultaneously pending select() calls */
#define MAXSELECTS 25
#define FROM_PROC 0
#define TO_PROC 1
#define USECPERSEC 1000000 /* number of microseconds in a second */
typedef fd_set *ixfer_fd_set_ptr;
static struct selectentry {
struct fproc *requestor; /* slot is free iff this is NULL */
endpoint_t req_endpt;
fd_set readfds, writefds, errorfds;
fd_set ready_readfds, ready_writefds, ready_errorfds;
ixfer_fd_set_ptr vir_readfds, vir_writefds, vir_errorfds;
struct filp *filps[OPEN_MAX];
int type[OPEN_MAX];
int nfds, nreadyfds;
int error;
char block;
char starting;
clock_t expiry;
minix_timer_t timer; /* if expiry > 0 */
} selecttab[MAXSELECTS];
static int copy_fdsets(struct selectentry *se, int nfds, int direction);
static void filp_status(struct filp *fp, int status);
static int is_deferred(struct selectentry *se);
static void restart_proc(struct selectentry *se);
static void ops2tab(int ops, int fd, struct selectentry *e);
static int is_regular_file(struct filp *f);
static int is_pipe(struct filp *f);
static int is_char_device(struct filp *f);
static int is_sock_device(struct filp *f);
static void select_lock_filp(struct filp *f, int ops);
static int select_request_file(struct filp *f, int *ops, int block,
struct fproc *rfp);
static int select_request_char(struct filp *f, int *ops, int block,
struct fproc *rfp);
static int select_request_sock(struct filp *f, int *ops, int block,
struct fproc *rfp);
static int select_request_pipe(struct filp *f, int *ops, int block,
struct fproc *rfp);
static void select_cancel_all(struct selectentry *e);
static void select_cancel_filp(struct filp *f);
static void select_return(struct selectentry *);
static void select_restart_filps(void);
static int tab2ops(int fd, struct selectentry *e);
static void wipe_select(struct selectentry *s);
void select_timeout_check(int s);
static struct fdtype {
int (*select_request)(struct filp *, int *ops, int block,
struct fproc *rfp);
int (*type_match)(struct filp *f);
} fdtypes[] = {
{ select_request_char, is_char_device },
{ select_request_sock, is_sock_device },
{ select_request_file, is_regular_file },
{ select_request_pipe, is_pipe },
};
#define SEL_FDS (sizeof(fdtypes) / sizeof(fdtypes[0]))
/*===========================================================================*
* do_select *
*===========================================================================*/
int do_select(void)
{
/* Implement the select(nfds, readfds, writefds, errorfds, timeout) system
* call. First we copy the arguments and verify their sanity. Then we check
* whether there are file descriptors that satisfy the select call right off
* the bat. If so, or if there are no ready file descriptors but the process
* requested to return immediately, we return the result. Otherwise we set a
* timeout and wait for either the file descriptors to become ready or the
* timer to go off. If no timeout value was provided, we wait indefinitely.
*/
int r, nfds, do_timeout, fd, type, s;
struct filp *f;
unsigned int ops;
struct timeval timeout;
struct selectentry *se;
vir_bytes vtimeout;
clock_t ticks;
nfds = job_m_in.m_lc_vfs_select.nfds;
vtimeout = job_m_in.m_lc_vfs_select.timeout;
/* Sane amount of file descriptors? */
if (nfds < 0 || nfds > OPEN_MAX) return(EINVAL);
/* Find a slot to store this select request */
for (s = 0; s < MAXSELECTS; s++)
if (selecttab[s].requestor == NULL) /* Unused slot */
break;
if (s >= MAXSELECTS) return(ENOSPC);
se = &selecttab[s];
wipe_select(se); /* Clear results of previous usage */
se->requestor = fp;
se->req_endpt = who_e;
se->vir_readfds = job_m_in.m_lc_vfs_select.readfds;
se->vir_writefds = job_m_in.m_lc_vfs_select.writefds;
se->vir_errorfds = job_m_in.m_lc_vfs_select.errorfds;
/* Copy fdsets from the process */
if ((r = copy_fdsets(se, nfds, FROM_PROC)) != OK) {
se->requestor = NULL;
return(r);
}
/* Did the process set a timeout value? If so, retrieve it. */
if (vtimeout != 0) {
r = sys_datacopy_wrapper(who_e, vtimeout, SELF, (vir_bytes) &timeout,
sizeof(timeout));
/* No nonsense in the timeval */
if (r == OK && (timeout.tv_sec < 0 || timeout.tv_usec < 0 ||
timeout.tv_usec >= USECPERSEC))
r = EINVAL;
if (r != OK) {
se->requestor = NULL;
return(r);
}
do_timeout = 1;
} else
do_timeout = 0;
/* If there is no timeout, we block forever. Otherwise, we block up to the
* specified time interval.
*/
if (!do_timeout) /* No timeout value set */
se->block = 1;
else if (do_timeout && (timeout.tv_sec > 0 || timeout.tv_usec > 0))
se->block = 1;
else /* timeout set as (0,0) - this effects a poll */
se->block = 0;
se->expiry = 0; /* no timer set (yet) */
/* We are going to lock filps, and that means that while locking a second
* filp, we might already get the results for the first one. In that case,
* the incoming results must not cause the select call to finish prematurely.
*/
se->starting = TRUE;
/* Verify that file descriptors are okay to select on */
for (fd = 0; fd < nfds; fd++) {
/* Because the select() interface implicitly includes file descriptors
* you might not want to select on, we have to figure out whether we're
* interested in them. Typically, these file descriptors include fd's
* inherited from the parent proc and file descriptors that have been
* close()d, but had a lower fd than one in the current set.
*/
if (!(ops = tab2ops(fd, se)))
continue; /* No operations set; nothing to do for this fd */
/* Get filp belonging to this fd. If this fails, there are two causes:
* either the given file descriptor was bad, or the associated filp is
* closed (in the FILP_CLOSED sense) as a result of invalidation. Only
* the former is a select error. The latter should result in operations
* being returned as ready on the file descriptor, since subsequent
* I/O calls are guaranteed to return I/O errors on such descriptors.
*/
f = se->filps[fd] = get_filp(fd, VNODE_READ);
if (f == NULL && err_code != EIO) {
assert(err_code == EBADF);
/* We may already have adjusted filp_selectors on previous
* file pointers in the set, so do not simply return here.
*/
se->error = EBADF;
break;
}
/* Check file types. According to POSIX 2008:
* "The pselect() and select() functions shall support regular files,
* terminal and pseudo-terminal devices, FIFOs, pipes, and sockets. The
* behavior of pselect() and select() on file descriptors that refer to
* other types of file is unspecified."
*
* In our case, terminal and pseudo-terminal devices are handled by the
* TTY and PTY character drivers respectively. Sockets are handled by
* by their respective socket drivers. Additionally, we give other
* character drivers the chance to handle select for any of their
* device nodes. Some may not implement support for select and let
* libchardriver return EBADF, which we then pass to the calling
* process once we receive the reply.
*
* If we could not access the file pointer at all, it will have been
* closed due to invalidation after a service crash. In that case, we
* skip type matching and simply return pending operations as ready.
*/
se->type[fd] = -1;
if (f == NULL)
continue; /* closed, skip type matching */
for (type = 0; type < SEL_FDS; type++) {
if (fdtypes[type].type_match(f)) {
se->type[fd] = type;
se->nfds = fd+1;
se->filps[fd]->filp_selectors++;
break;
}
}
unlock_filp(f);
if (se->type[fd] == -1) { /* Type not found */
se->error = EBADF;
break;
}
}
/* If an error occurred already, undo any changes so far and return. */
if (se->error != OK) {
select_cancel_all(se);
se->requestor = NULL;
return(se->error);
}
/* Check all file descriptors in the set whether one is 'ready' now */
for (fd = 0; fd < nfds; fd++) {
/* Again, check for involuntarily selected fd's */
if (!(ops = tab2ops(fd, se)))
continue; /* No operations set; nothing to do for this fd */
/* File descriptors selected for reading that are not opened for
* reading should be marked as readable, as read calls would fail
* immediately. The same applies to writing. For file descriptors for
* which the file pointer is already closed (f==NULL), return readable
* and writable operations (if requested) and skip the rest.
*/
f = se->filps[fd];
if (f == NULL) {
ops2tab(SEL_RD | SEL_WR, fd, se);
continue;
}
if ((ops & SEL_RD) && !(f->filp_mode & R_BIT)) {
ops2tab(SEL_RD, fd, se);
ops &= ~SEL_RD;
}
if ((ops & SEL_WR) && !(f->filp_mode & W_BIT)) {
ops2tab(SEL_WR, fd, se);
ops &= ~SEL_WR;
}
/* Test filp for select operations if not already done so. e.g.,
* processes sharing a filp and both doing a select on that filp. */
if ((f->filp_select_ops & ops) != ops) {
int wantops;
wantops = (f->filp_select_ops |= ops);
type = se->type[fd];
assert(type >= 0);
select_lock_filp(f, wantops);
r = fdtypes[type].select_request(f, &wantops, se->block, fp);
unlock_filp(f);
if (r != OK && r != SUSPEND) {
se->error = r;
break; /* Error or bogus return code; abort */
}
/* The select request above might have turned on/off some
* operations because they were 'ready' or not meaningful.
* Either way, we might have a result and we need to store them
* in the select table entry. */
if (wantops & ops) ops2tab(wantops, fd, se);
}
}
/* At this point there won't be any blocking calls anymore. */
se->starting = FALSE;
if ((se->nreadyfds > 0 || se->error != OK || !se->block) &&
!is_deferred(se)) {
/* An error occurred, or fd's were found that were ready to go right
* away, and/or we were instructed not to block at all. Must return
* immediately. Do not copy FD sets if an error occurred.
*/
if (se->error != OK)
r = se->error;
else
r = copy_fdsets(se, se->nfds, TO_PROC);
select_cancel_all(se);
se->requestor = NULL;
if (r != OK)
return(r);
return(se->nreadyfds);
}
/* Convert timeval to ticks and set the timer. If it fails, undo
* all, return error.
*/
if (do_timeout && se->block) {
/* Open Group:
* "If the requested timeout interval requires a finer
* granularity than the implementation supports, the
* actual timeout interval shall be rounded up to the next
* supported value."
*/
if (timeout.tv_sec >= (TMRDIFF_MAX - 1) / system_hz) {
ticks = TMRDIFF_MAX; /* silently truncate */
} else {
ticks = timeout.tv_sec * system_hz +
(timeout.tv_usec * system_hz + USECPERSEC-1) / USECPERSEC;
}
assert(ticks != 0 && ticks <= TMRDIFF_MAX);
se->expiry = ticks;
set_timer(&se->timer, ticks, select_timeout_check, s);
}
/* process now blocked */
suspend(FP_BLOCKED_ON_SELECT);
return(SUSPEND);
}
/*===========================================================================*
* is_deferred *
*===========================================================================*/
static int is_deferred(struct selectentry *se)
{
/* Find out whether this select has pending initial replies */
int fd;
struct filp *f;
/* The select call must have finished its initialization at all. */
if (se->starting) return(TRUE);
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL) continue;
if (f->filp_select_flags & (FSF_UPDATE|FSF_BUSY)) return(TRUE);
}
return(FALSE);
}
/*===========================================================================*
* is_regular_file *
*===========================================================================*/
static int is_regular_file(struct filp *f)
{
return(f && f->filp_vno && S_ISREG(f->filp_vno->v_mode));
}
/*===========================================================================*
* is_pipe *
*===========================================================================*/
static int is_pipe(struct filp *f)
{
/* Recognize either anonymous pipe or named pipe (FIFO) */
return(f && f->filp_vno && S_ISFIFO(f->filp_vno->v_mode));
}
/*===========================================================================*
* is_char_device *
*===========================================================================*/
static int is_char_device(struct filp *f)
{
/* See if this filp is a handle on a character device. This function MUST NOT
* block its calling thread. The given filp may or may not be locked.
*/
return (f && f->filp_vno && S_ISCHR(f->filp_vno->v_mode));
}
/*===========================================================================*
* is_sock_device *
*===========================================================================*/
static int is_sock_device(struct filp *f)
{
/* See if this filp is a handle on a socket device. This function MUST NOT
* block its calling thread. The given filp may or may not be locked.
*/
return (f && f->filp_vno && S_ISSOCK(f->filp_vno->v_mode));
}
/*===========================================================================*
* select_filter *
*===========================================================================*/
static int select_filter(struct filp *f, int *ops, int block)
{
/* Determine which select operations can be satisfied immediately and which
* should be requested. Used for character and socket devices. This function
* MUST NOT block its calling thread.
*/
int rops;
rops = *ops;
/* By default, nothing to do */
*ops = 0;
/*
* If we have previously asked the driver to notify us about certain ready
* operations, but it has not notified us yet, then we can safely assume that
* those operations are not ready right now. Therefore, if this call is not
* supposed to block, we can disregard the pending operations as not ready.
* We must make absolutely sure that the flags are "stable" right now though:
* we are neither waiting to query the driver about them (FSF_UPDATE) nor
* querying the driver about them right now (FSF_BUSY). This is a dangerous
* case of premature optimization and may be removed altogether if it proves
* to continue to be a source of bugs.
*/
if (!block && !(f->filp_select_flags & (FSF_UPDATE | FSF_BUSY)) &&
(f->filp_select_flags & FSF_BLOCKED)) {
if ((rops & SEL_RD) && (f->filp_select_flags & FSF_RD_BLOCK))
rops &= ~SEL_RD;
if ((rops & SEL_WR) && (f->filp_select_flags & FSF_WR_BLOCK))
rops &= ~SEL_WR;
if ((rops & SEL_ERR) && (f->filp_select_flags & FSF_ERR_BLOCK))
rops &= ~SEL_ERR;
if (!(rops & (SEL_RD|SEL_WR|SEL_ERR)))
return(0);
}
f->filp_select_flags |= FSF_UPDATE;
if (block) {
rops |= SEL_NOTIFY;
if (rops & SEL_RD) f->filp_select_flags |= FSF_RD_BLOCK;
if (rops & SEL_WR) f->filp_select_flags |= FSF_WR_BLOCK;
if (rops & SEL_ERR) f->filp_select_flags |= FSF_ERR_BLOCK;
}
if (f->filp_select_flags & FSF_BUSY)
return(SUSPEND);
return rops;
}
/*===========================================================================*
* select_request_char *
*===========================================================================*/
static int select_request_char(struct filp *f, int *ops, int block,
struct fproc *rfp)
{
/* Check readiness status on a character device. Unless suitable results are
* available right now, this will only initiate the polling process, causing
* result processing to be deferred. This function MUST NOT block its calling
* thread. The given filp may or may not be locked.
*/
dev_t dev;
int r, rops;
struct dmap *dp;
/* Start by remapping the device node number to a "real" device number. Those
* two are different only for CTTY_MAJOR aka /dev/tty, but that one single
* exception requires quite some extra effort here: the select code matches
* character driver replies to their requests based on the device number, so
* it needs to be aware that device numbers may be mapped. The idea is to
* perform the mapping once and store the result in the filp object, so that
* at least we don't run into problems when a process loses its controlling
* terminal while doing a select (see also free_proc). It should be noted
* that it is possible that multiple processes share the same /dev/tty filp,
* and they may not all have a controlling terminal. The ctty-less processes
* should never pass the mapping; a more problematic case is checked below.
*
* The cdev_map call also checks the major number for rough validity, so that
* we can use it to index the dmap array safely a bit later.
*/
if ((dev = cdev_map(f->filp_vno->v_sdev, rfp)) == NO_DEV)
return(ENXIO);
if (f->filp_select_dev != NO_DEV && f->filp_select_dev != dev) {
/* Currently, this case can occur as follows: a process with a
* controlling terminal opens /dev/tty and forks, the new child starts
* a new session, opens a new controlling terminal, and both parent and
* child call select on the /dev/tty file descriptor. If this case ever
* becomes real, a better solution may be to force-close a filp for
* /dev/tty when a new controlling terminal is opened.
*/
printf("VFS: file pointer has multiple controlling TTYs!\n");
return(EIO);
}
f->filp_select_dev = dev; /* set before possibly suspending */
if ((rops = select_filter(f, ops, block)) <= 0)
return(rops); /* OK or suspend: nothing to do for now */
dp = &dmap[major(dev)];
if (dp->dmap_sel_busy)
return(SUSPEND);
f->filp_select_flags &= ~FSF_UPDATE;
r = cdev_select(dev, rops);
if (r != OK)
return(r);
dp->dmap_sel_busy = TRUE;
dp->dmap_sel_filp = f;
f->filp_select_flags |= FSF_BUSY;
return(SUSPEND);
}
/*===========================================================================*
* select_request_sock *
*===========================================================================*/
static int select_request_sock(struct filp *f, int *ops, int block,
struct fproc *rfp __unused)
{
/* Check readiness status on a socket device. Unless suitable results are
* available right now, this will only initiate the polling process, causing
* result processing to be deferred. This function MUST NOT block its calling
* thread. The given filp may or may not be locked.
*/
struct smap *sp;
dev_t dev;
int r, rops;
dev = f->filp_vno->v_sdev;
if ((sp = get_smap_by_dev(dev, NULL)) == NULL)
return(ENXIO); /* this should not happen */
f->filp_select_dev = dev; /* set before possibly suspending */
if ((rops = select_filter(f, ops, block)) <= 0)
return(rops); /* OK or suspend: nothing to do for now */
if (sp->smap_sel_busy)
return(SUSPEND);
f->filp_select_flags &= ~FSF_UPDATE;
r = sdev_select(dev, rops);
if (r != OK)
return(r);
sp->smap_sel_busy = TRUE;
sp->smap_sel_filp = f;
f->filp_select_flags |= FSF_BUSY;
return(SUSPEND);
}
/*===========================================================================*
* select_request_file *
*===========================================================================*/
static int select_request_file(struct filp *UNUSED(f), int *UNUSED(ops),
int UNUSED(block), struct fproc *UNUSED(rfp))
{
/* Files are always ready, so output *ops is input *ops */
return(OK);
}
/*===========================================================================*
* select_request_pipe *
*===========================================================================*/
static int select_request_pipe(struct filp *f, int *ops, int block,
struct fproc *UNUSED(rfp))
{
/* Check readiness status on a pipe. The given filp is locked. This function
* may block its calling thread if necessary.
*/
int orig_ops, r = 0, err;
orig_ops = *ops;
if ((*ops & (SEL_RD|SEL_ERR))) {
/* Check if we can read 1 byte */
err = pipe_check(f, READING, f->filp_flags & ~O_NONBLOCK, 1,
1 /* Check only */);
if (err != SUSPEND)
r |= SEL_RD;
if (err < 0 && err != SUSPEND)
r |= SEL_ERR;
}
if ((*ops & (SEL_WR|SEL_ERR))) {
/* Check if we can write 1 byte */
err = pipe_check(f, WRITING, f->filp_flags & ~O_NONBLOCK, 1,
1 /* Check only */);
if (err != SUSPEND)
r |= SEL_WR;
if (err < 0 && err != SUSPEND)
r |= SEL_ERR;
}
/* Some options we collected might not be requested. */
*ops = r & orig_ops;
if (!*ops && block)
f->filp_pipe_select_ops |= orig_ops;
return(OK);
}
/*===========================================================================*
* tab2ops *
*===========================================================================*/
static int tab2ops(int fd, struct selectentry *e)
{
int ops = 0;
if (FD_ISSET(fd, &e->readfds)) ops |= SEL_RD;
if (FD_ISSET(fd, &e->writefds)) ops |= SEL_WR;
if (FD_ISSET(fd, &e->errorfds)) ops |= SEL_ERR;
return(ops);
}
/*===========================================================================*
* ops2tab *
*===========================================================================*/
static void ops2tab(int ops, int fd, struct selectentry *e)
{
if ((ops & SEL_RD) && e->vir_readfds && FD_ISSET(fd, &e->readfds) &&
!FD_ISSET(fd, &e->ready_readfds)) {
FD_SET(fd, &e->ready_readfds);
e->nreadyfds++;
}
if ((ops & SEL_WR) && e->vir_writefds && FD_ISSET(fd, &e->writefds) &&
!FD_ISSET(fd, &e->ready_writefds)) {
FD_SET(fd, &e->ready_writefds);
e->nreadyfds++;
}
if ((ops & SEL_ERR) && e->vir_errorfds && FD_ISSET(fd, &e->errorfds) &&
!FD_ISSET(fd, &e->ready_errorfds)) {
FD_SET(fd, &e->ready_errorfds);
e->nreadyfds++;
}
}
/*===========================================================================*
* copy_fdsets *
*===========================================================================*/
static int copy_fdsets(struct selectentry *se, int nfds, int direction)
{
/* Copy FD sets from or to the user process calling select(2). This function
* MUST NOT block the calling thread.
*/
int r;
size_t fd_setsize;
endpoint_t src_e, dst_e;
fd_set *src_fds, *dst_fds;
if (nfds < 0 || nfds > OPEN_MAX)
panic("select copy_fdsets: nfds wrong: %d", nfds);
/* Only copy back as many bits as the user expects. */
fd_setsize = (size_t) (howmany(nfds, __NFDBITS) * sizeof(__fd_mask));
/* Set source and destination endpoints */
src_e = (direction == FROM_PROC) ? se->req_endpt : SELF;
dst_e = (direction == FROM_PROC) ? SELF : se->req_endpt;
/* read set */
src_fds = (direction == FROM_PROC) ? se->vir_readfds : &se->ready_readfds;
dst_fds = (direction == FROM_PROC) ? &se->readfds : se->vir_readfds;
if (se->vir_readfds) {
r = sys_datacopy_wrapper(src_e, (vir_bytes) src_fds, dst_e,
(vir_bytes) dst_fds, fd_setsize);
if (r != OK) return(r);
}
/* write set */
src_fds = (direction == FROM_PROC) ? se->vir_writefds : &se->ready_writefds;
dst_fds = (direction == FROM_PROC) ? &se->writefds : se->vir_writefds;
if (se->vir_writefds) {
r = sys_datacopy_wrapper(src_e, (vir_bytes) src_fds, dst_e,
(vir_bytes) dst_fds, fd_setsize);
if (r != OK) return(r);
}
/* error set */
src_fds = (direction == FROM_PROC) ? se->vir_errorfds : &se->ready_errorfds;
dst_fds = (direction == FROM_PROC) ? &se->errorfds : se->vir_errorfds;
if (se->vir_errorfds) {
r = sys_datacopy_wrapper(src_e, (vir_bytes) src_fds, dst_e,
(vir_bytes) dst_fds, fd_setsize);
if (r != OK) return(r);
}
return(OK);
}
/*===========================================================================*
* select_cancel_all *
*===========================================================================*/
static void select_cancel_all(struct selectentry *se)
{
/* Cancel select, possibly on success. Decrease select usage and cancel timer.
* This function MUST NOT block its calling thread.
*/
int fd;
struct filp *f;
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL) continue;
se->filps[fd] = NULL;
select_cancel_filp(f);
}
if (se->expiry > 0) {
cancel_timer(&se->timer);
se->expiry = 0;
}
se->requestor = NULL;
}
/*===========================================================================*
* select_cancel_filp *
*===========================================================================*/
static void select_cancel_filp(struct filp *f)
{
/* Reduce the number of select users of this filp. This function MUST NOT block
* its calling thread.
*/
devmajor_t major;
struct smap *sp;
assert(f);
assert(f->filp_selectors > 0);
assert(f->filp_count > 0);
f->filp_selectors--;
if (f->filp_selectors == 0) {
/* No one selecting on this filp anymore, forget about select state */
f->filp_select_ops = 0;
f->filp_select_flags = 0;
f->filp_pipe_select_ops = 0;
/* If this filp is the subject of an ongoing select query to a
* character or socket device, mark the query as stale, so that this
* filp will not be checked when the result arrives. The filp select
* device may still be NO_DEV if do_select fails on the initial fd
* check.
*/
if (is_char_device(f) && f->filp_select_dev != NO_DEV) {
major = major(f->filp_select_dev);
if (dmap[major].dmap_sel_busy &&
dmap[major].dmap_sel_filp == f)
dmap[major].dmap_sel_filp = NULL; /* leave _busy set */
f->filp_select_dev = NO_DEV;
} else if (is_sock_device(f) && f->filp_select_dev != NO_DEV) {
if ((sp = get_smap_by_dev(f->filp_select_dev, NULL)) != NULL &&
sp->smap_sel_busy && sp->smap_sel_filp == f)
sp->smap_sel_filp = NULL; /* leave _busy set */
f->filp_select_dev = NO_DEV;
}
}
}
/*===========================================================================*
* select_return *
*===========================================================================*/
static void select_return(struct selectentry *se)
{
/* Return the results of a select call to the user process and revive the
* process. This function MUST NOT block its calling thread.
*/
int r;
assert(!is_deferred(se)); /* Not done yet, first wait for async reply */
select_cancel_all(se);
if (se->error != OK)
r = se->error;
else
r = copy_fdsets(se, se->nfds, TO_PROC);
if (r == OK)
r = se->nreadyfds;
revive(se->req_endpt, r);
}
/*===========================================================================*
* select_callback *
*===========================================================================*/
void select_callback(struct filp *f, int status)
{
/* The status of a filp has changed, with the given ready operations or error.
* This function is currently called only for pipes, and holds the lock to
* the filp.
*/
filp_status(f, status);
}
/*===========================================================================*
* init_select *
*===========================================================================*/
void init_select(void)
{
int s;
for (s = 0; s < MAXSELECTS; s++)
init_timer(&selecttab[s].timer);
}
/*===========================================================================*
* select_forget *
*===========================================================================*/
void select_forget(void)
{
/* The calling thread's associated process is expected to be unpaused, due to
* a signal that is supposed to interrupt the current system call. Totally
* forget about the select(). This function may block its calling thread if
* necessary (but it doesn't).
*/
int slot;
struct selectentry *se;
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == fp)
break;
}
if (slot >= MAXSELECTS) return; /* Entry not found */
assert(se->starting == FALSE);
/* Do NOT test on is_deferred here. We can safely cancel ongoing queries. */
select_cancel_all(se);
}
/*===========================================================================*
* select_timeout_check *
*===========================================================================*/
void select_timeout_check(int s)
{
/* An alarm has gone off for one of the select queries. This function MUST NOT
* block its calling thread.
*/
struct selectentry *se;
if (s < 0 || s >= MAXSELECTS) return; /* Entry does not exist */
se = &selecttab[s];
if (se->requestor == NULL) return;
if (se->expiry == 0) return; /* Strange, did we even ask for a timeout? */
se->expiry = 0;
if (!is_deferred(se))
select_return(se);
else
se->block = 0; /* timer triggered "too soon", treat as nonblocking */
}
/*===========================================================================*
* select_unsuspend_by_endpt *
*===========================================================================*/
void select_unsuspend_by_endpt(endpoint_t proc_e)
{
/* Revive blocked processes when a driver has disappeared */
struct dmap *dp;
struct smap *sp;
devmajor_t major;
int fd, s, is_driver, restart;
struct selectentry *se;
struct filp *f;
/* Either or both of these may be NULL. */
dp = get_dmap_by_endpt(proc_e);
sp = get_smap_by_endpt(proc_e);
is_driver = (dp != NULL || sp != NULL);
for (s = 0; s < MAXSELECTS; s++) {
se = &selecttab[s];
if (se->requestor == NULL) continue;
if (se->requestor->fp_endpoint == proc_e) {
assert(se->requestor->fp_flags & FP_EXITING);
select_cancel_all(se);
continue;
}
/* Skip the more expensive "driver died" checks for non-drivers. */
if (!is_driver)
continue;
restart = FALSE;
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL)
continue;
if (is_char_device(f)) {
assert(f->filp_select_dev != NO_DEV);
major = major(f->filp_select_dev);
if (dmap_driver_match(proc_e, major)) {
ops2tab(SEL_RD | SEL_WR, fd, se);
se->filps[fd] = NULL;
select_cancel_filp(f);
restart = TRUE;
}
} else if (sp != NULL && is_sock_device(f)) {
assert(f->filp_select_dev != NO_DEV);
if (get_smap_by_dev(f->filp_select_dev, NULL) == sp) {
ops2tab(SEL_RD | SEL_WR, fd, se);
se->filps[fd] = NULL;
select_cancel_filp(f);
restart = TRUE;
}
}
}
if (restart)
restart_proc(se);
}
/* Any outstanding queries will never be answered, so forget about them. */
if (dp != NULL) {
assert(dp->dmap_sel_filp == NULL);
dp->dmap_sel_busy = FALSE;
}
if (sp != NULL) {
assert(sp->smap_sel_filp == NULL);
sp->smap_sel_busy = FALSE;
}
}
/*===========================================================================*
* select_reply1 *
*===========================================================================*/
static void select_reply1(struct filp *f, int status)
{
/* Handle the initial reply to a character or socket select request. This
* function MUST NOT block its calling thread.
*/
assert(f->filp_count >= 1);
assert(f->filp_select_flags & FSF_BUSY);
f->filp_select_flags &= ~FSF_BUSY;
/* The select call is done now, except when
* - another process started a select on the same filp with possibly a
* different set of operations.
* - a process does a select on the same filp but using different file
* descriptors.
* - the select has a timeout. Upon receiving this reply the operations
* might not be ready yet, so we want to wait for that to ultimately
* happen.
* Therefore we need to keep remembering what the operations are.
*/
if (!(f->filp_select_flags & (FSF_UPDATE|FSF_BLOCKED)))
f->filp_select_ops = 0; /* done selecting */
else if (status > 0 && !(f->filp_select_flags & FSF_UPDATE))
/* there may be operations pending */
f->filp_select_ops &= ~status;
/* Record new filp status */
if (!(status == 0 && (f->filp_select_flags & FSF_BLOCKED))) {
if (status > 0) { /* operations ready */
if (status & SEL_RD)
f->filp_select_flags &= ~FSF_RD_BLOCK;
if (status & SEL_WR)
f->filp_select_flags &= ~FSF_WR_BLOCK;
if (status & SEL_ERR)
f->filp_select_flags &= ~FSF_ERR_BLOCK;
} else if (status < 0) { /* error */
/* Always unblock upon error */
f->filp_select_flags &= ~FSF_BLOCKED;
}
}
filp_status(f, status); /* Tell filp owners about the results */
}
/*===========================================================================*
* select_cdev_reply1 *
*===========================================================================*/
void select_cdev_reply1(endpoint_t driver_e, devminor_t minor, int status)
{
/* Handle the initial reply to a CDEV_SELECT request. This function MUST NOT
* block its calling thread.
*/
devmajor_t major;
dev_t dev;
struct filp *f;
struct dmap *dp;
/* Figure out which device is replying */
if ((dp = get_dmap_by_endpt(driver_e)) == NULL) return;
major = dp-dmap;
dev = makedev(major, minor);
/* Get filp belonging to character special file */
if (!dp->dmap_sel_busy) {
printf("VFS (%s:%d): major %d was not expecting a CDEV_SELECT reply\n",
__FILE__, __LINE__, major);
return;
}
/* The select filp may have been set to NULL if the requestor has been
* unpaused in the meantime. In that case, we ignore the result, but we do
* look for other filps to restart later.
*/
if ((f = dp->dmap_sel_filp) != NULL) {
/* Find vnode and check we got a reply from the device we expected */
assert(is_char_device(f));
assert(f->filp_select_dev != NO_DEV);
if (f->filp_select_dev != dev) {
/* This should never happen. The driver may be misbehaving.
* For now we assume that the reply we want will arrive later..
*/
printf("VFS (%s:%d): expected reply from dev %llx not %llx\n",
__FILE__, __LINE__, f->filp_select_dev, dev);
return;
}
}
/* No longer waiting for a reply from this device */
dp->dmap_sel_busy = FALSE;
dp->dmap_sel_filp = NULL;
/* Process the status change, if still applicable. */
if (f != NULL)
select_reply1(f, status);
/* See if we should send a select request for another filp now. */
select_restart_filps();
}
/*===========================================================================*
* select_sdev_reply1 *
*===========================================================================*/
void select_sdev_reply1(dev_t dev, int status)
{
/* Handle the initial reply to a SDEV_SELECT request. This function MUST NOT
* block its calling thread.
*/
struct smap *sp;
struct filp *f;
if ((sp = get_smap_by_dev(dev, NULL)) == NULL)
return;
/* Get the file pointer for the socket device. */
if (!sp->smap_sel_busy) {
printf("VFS: was not expecting a SDEV_SELECT reply from %d\n",
sp->smap_endpt);
return;
}
/* The select filp may have been set to NULL if the requestor has been
* unpaused in the meantime. In that case, we ignore the result, but we do
* look for other filps to restart later.
*/
if ((f = sp->smap_sel_filp) != NULL) {
/* Find vnode and check we got a reply from the device we expected */
assert(is_sock_device(f));
assert(f->filp_select_dev != NO_DEV);
if (f->filp_select_dev != dev) {
/* This should never happen. The driver may be misbehaving.
* For now we assume that the reply we want will arrive later..
*/
printf("VFS: expected reply from sock dev %llx, not %llx\n",
f->filp_select_dev, dev);
return;
}
}
/* We are no longer waiting for a reply from this socket driver. */
sp->smap_sel_busy = FALSE;
sp->smap_sel_filp = NULL;
/* Process the status change, if still applicable. */
if (f != NULL)
select_reply1(f, status);
/* See if we should send a select request for another filp now. */
select_restart_filps();
}
/*===========================================================================*
* select_reply2 *
*===========================================================================*/
static void select_reply2(int is_char, dev_t dev, int status)
{
/* Find all file descriptors selecting for the given character (is_char==TRUE)
* or socket (is_char==FALSE) device, update their statuses, and resume
* activities accordingly.
*/
int slot, found, fd;
struct filp *f;
struct selectentry *se;
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == NULL) continue; /* empty slot */
found = FALSE;
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL) continue;
if (is_char && !is_char_device(f)) continue;
if (!is_char && !is_sock_device(f)) continue;
assert(f->filp_select_dev != NO_DEV);
if (f->filp_select_dev != dev) continue;
if (status > 0) { /* Operations ready */
/* Clear the replied bits from the request
* mask unless FSF_UPDATE is set.
*/
if (!(f->filp_select_flags & FSF_UPDATE))
f->filp_select_ops &= ~status;
if (status & SEL_RD)
f->filp_select_flags &= ~FSF_RD_BLOCK;
if (status & SEL_WR)
f->filp_select_flags &= ~FSF_WR_BLOCK;
if (status & SEL_ERR)
f->filp_select_flags &= ~FSF_ERR_BLOCK;
ops2tab(status, fd, se);
} else {
f->filp_select_flags &= ~FSF_BLOCKED;
se->error = status;
}
found = TRUE;
}
/* Even if 'found' is set now, nothing may have changed for this call,
* as it may not have been interested in the operations that were
* reported as ready. Let restart_proc check.
*/
if (found)
restart_proc(se);
}
select_restart_filps();
}
/*===========================================================================*
* select_cdev_reply2 *
*===========================================================================*/
void select_cdev_reply2(endpoint_t driver_e, devminor_t minor, int status)
{
/* Handle a secondary reply to a CDEV_SELECT request. A secondary reply occurs
* when the select request is 'blocking' until an operation becomes ready. This
* function MUST NOT block its calling thread.
*/
devmajor_t major;
struct dmap *dp;
dev_t dev;
if (status == 0) {
printf("VFS (%s:%d): weird status (%d) to report\n",
__FILE__, __LINE__, status);
return;
}
/* Figure out which device is replying */
if ((dp = get_dmap_by_endpt(driver_e)) == NULL) {
printf("VFS (%s:%d): endpoint %d is not a known driver endpoint\n",
__FILE__, __LINE__, driver_e);
return;
}
major = dp-dmap;
dev = makedev(major, minor);
select_reply2(TRUE /*is_char*/, dev, status);
}
/*===========================================================================*
* select_sdev_reply2 *
*===========================================================================*/
void select_sdev_reply2(dev_t dev, int status)
{
/* Handle a secondary reply to a SDEV_SELECT request. A secondary reply occurs
* when the select request is 'blocking' until an operation becomes ready. This
* function MUST NOT block its calling thread.
*/
if (status == 0) {
printf("VFS: weird socket device status (%d)\n", status);
return;
}
select_reply2(FALSE /*is_char*/, dev, status);
}
/*===========================================================================*
* select_restart_filps *
*===========================================================================*/
static void select_restart_filps(void)
{
/* We got a result from a character driver, and now we need to check if we can
* restart deferred polling operations. This function MUST NOT block its
* calling thread.
*/
int fd, slot;
struct filp *f;
struct selectentry *se;
/* Locate filps that can be restarted */
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == NULL) continue; /* empty slot */
/* Only 'deferred' processes are eligible to restart */
if (!is_deferred(se)) continue;
/* Find filps that are not waiting for a reply, but have an updated
* status (i.e., another select on the same filp with possibly a
* different set of operations is to be done), and thus requires the
* select request to be sent again).
*/
for (fd = 0; fd < se->nfds; fd++) {
int r, wantops, ops;
if ((f = se->filps[fd]) == NULL) continue;
if (f->filp_select_flags & FSF_BUSY) /* Still waiting for */
continue; /* initial reply */
if (!(f->filp_select_flags & FSF_UPDATE)) /* Must be in */
continue; /* 'update' state */
/* This function is suitable only for character and socket
* devices. In particular, checking pipes the same way would
* introduce a serious locking problem.
*/
assert(is_char_device(f) || is_sock_device(f));
wantops = ops = f->filp_select_ops;
if (is_char_device(f))
r = select_request_char(f, &wantops, se->block,
se->requestor);
else
r = select_request_sock(f, &wantops, se->block,
se->requestor);
if (r != OK && r != SUSPEND) {
se->error = r;
restart_proc(se);
break; /* Error or bogus return code; abort */
}
if (wantops & ops) ops2tab(wantops, fd, se);
}
}
}
/*===========================================================================*
* filp_status *
*===========================================================================*/
static void
filp_status(struct filp *f, int status)
{
/* Tell processes that need to know about the status of this filp. This
* function MUST NOT block its calling thread.
*/
int fd, slot, found;
struct selectentry *se;
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == NULL) continue; /* empty slot */
found = FALSE;
for (fd = 0; fd < se->nfds; fd++) {
if (se->filps[fd] != f) continue;
if (status < 0)
se->error = status;
else
ops2tab(status, fd, se);
found = TRUE;
}
if (found)
restart_proc(se);
}
}
/*===========================================================================*
* restart_proc *
*===========================================================================*/
static void
restart_proc(struct selectentry *se)
{
/* Tell process about select results (if any) unless there are still results
* pending. This function MUST NOT block its calling thread.
*/
if ((se->nreadyfds > 0 || se->error != OK || !se->block) && !is_deferred(se))
select_return(se);
}
/*===========================================================================*
* wipe_select *
*===========================================================================*/
static void wipe_select(struct selectentry *se)
{
se->nfds = 0;
se->nreadyfds = 0;
se->error = OK;
se->block = 0;
memset(se->filps, 0, sizeof(se->filps));
FD_ZERO(&se->readfds);
FD_ZERO(&se->writefds);
FD_ZERO(&se->errorfds);
FD_ZERO(&se->ready_readfds);
FD_ZERO(&se->ready_writefds);
FD_ZERO(&se->ready_errorfds);
}
/*===========================================================================*
* select_lock_filp *
*===========================================================================*/
static void select_lock_filp(struct filp *f, int ops)
{
/* Lock a filp and vnode based on which operations are requested. This function
* may block its calling thread, obviously.
*/
tll_access_t locktype;
locktype = VNODE_READ; /* By default */
if (ops & (SEL_WR|SEL_ERR))
/* Selecting for error or writing requires exclusive access */
locktype = VNODE_WRITE;
lock_filp(f, locktype);
}
/*
* Dump the state of the entire select table, for debugging purposes.
*/
void
select_dump(void)
{
struct selectentry *se;
struct filp *f;
struct dmap *dp;
struct smap *sp;
dev_t dev;
sockid_t sockid;
int s, fd;
for (s = 0; s < MAXSELECTS; s++) {
se = &selecttab[s];
if (se->requestor == NULL)
continue;
printf("select %d: endpt %d nfds %d nreadyfds %d error %d "
"block %d starting %d expiry %u is_deferred %d\n",
s, se->req_endpt, se->nfds, se->nreadyfds, se->error,
se->block, se->starting, se->expiry, is_deferred(se));
for (fd = 0; !se->starting && fd < se->nfds; fd++) {
/* Save on output: do not print NULL filps at all. */
if ((f = se->filps[fd]) == NULL)
continue;
printf("- [%d] filp %p flags %x type ", fd, f,
f->filp_select_flags);
if (is_regular_file(f))
printf("regular\n");
else if (is_pipe(f))
printf("pipe\n");
else if (is_char_device(f)) {
dev = cdev_map(f->filp_vno->v_sdev,
se->requestor);
printf("char (dev <%d,%d>, dmap ",
major(dev), minor(dev));
if (dev != NO_DEV) {
dp = &dmap[major(dev)];
printf("busy %d filp %p)\n",
dp->dmap_sel_busy,
dp->dmap_sel_filp);
} else
printf("unknown)\n");
} else if (is_sock_device(f)) {
dev = f->filp_vno->v_sdev;
printf("sock (dev ");
sp = get_smap_by_dev(dev, &sockid);
if (sp != NULL) {
printf("<%d,%d>, smap busy %d filp "
"%p)\n", sp->smap_num, sockid,
sp->smap_sel_busy,
sp->smap_sel_filp);
} else
printf("<0x%"PRIx64">, smap "
"unknown)\n", dev);
} else
printf("unknown\n");
}
}
}
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