128 lines
2.6 KiB
C
128 lines
2.6 KiB
C
#include <assert.h>
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#include <errno.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/stat.h>
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#include <sys/uio.h>
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#include <unistd.h>
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#define VECTORIO_READ 1
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#define VECTORIO_WRITE 2
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#define MIN(x, y) (((x) < (y)) ? (x) : (y))
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static ssize_t vectorio_buffer(int fildes, const struct iovec *iov,
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int iovcnt, int readwrite, ssize_t totallen)
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{
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char *buffer;
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int iovidx, errno_saved;
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ssize_t copied, len, r;
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/* allocate buffer */
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buffer = (char *) malloc(totallen);
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if (!buffer)
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return -1;
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/* perform the actual read/write for the entire buffer */
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switch (readwrite)
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{
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case VECTORIO_READ:
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/* first read, then copy buffers (only part read) */
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r = read(fildes, buffer, totallen);
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copied = 0;
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iovidx = 0;
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while (copied < r)
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{
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assert(iovidx < iovcnt);
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len = MIN(r - copied, iov[iovidx].iov_len);
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memcpy(iov[iovidx++].iov_base, buffer + copied, len);
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copied += len;
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}
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assert(r < 0 || r == copied);
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break;
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case VECTORIO_WRITE:
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/* first copy buffers, then write */
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copied = 0;
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for (iovidx = 0; iovidx < iovcnt; iovidx++)
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{
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memcpy(buffer + copied, iov[iovidx].iov_base,
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iov[iovidx].iov_len);
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copied += iov[iovidx].iov_len;
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}
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assert(copied == totallen);
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r = write(fildes, buffer, totallen);
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break;
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default:
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assert(0);
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errno = EINVAL;
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r = -1;
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}
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/* free the buffer, keeping errno unchanged */
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errno_saved = errno;
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free(buffer);
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errno = errno_saved;
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return r;
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}
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static ssize_t vectorio(int fildes, const struct iovec *iov,
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int iovcnt, int readwrite)
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{
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int i;
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ssize_t totallen;
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/* parameter sanity checks */
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if (iovcnt > IOV_MAX)
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{
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errno = EINVAL;
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return -1;
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}
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totallen = 0;
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for (i = 0; i < iovcnt; i++)
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{
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/* don't read/write anything in case of possible overflow */
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if ((ssize_t) (totallen + iov[i].iov_len) < totallen)
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{
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errno = EINVAL;
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return -1;
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}
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totallen += iov[i].iov_len;
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/* report on NULL pointers */
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if (iov[i].iov_len && !iov[i].iov_base)
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{
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errno = EFAULT;
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return -1;
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}
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}
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/* anything to do? */
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if (totallen == 0)
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return 0;
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/*
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* there aught to be a system call here; instead we use an intermediate
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* buffer; this is preferred over multiple read/write calls because
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* this function has to be atomic
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*/
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return vectorio_buffer(fildes, iov, iovcnt, readwrite, totallen);
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}
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ssize_t readv(int fildes, const struct iovec *iov, int iovcnt)
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{
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return vectorio(fildes, iov, iovcnt, VECTORIO_READ);
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}
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ssize_t writev(int fildes, const struct iovec *iov, int iovcnt)
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{
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return vectorio(fildes, iov, iovcnt, VECTORIO_WRITE);
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}
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