This patch adds (very limited) support for memory-mapping pages on
file systems that are mounted on the special "none" device and that
do not implement PEEK support by themselves. This includes hgfs,
vbfs, and procfs.
The solution is implemented in libvtreefs, and consists of allocating
pages, filling them with content by calling the file system's READ
functionality, passing the pages to VM, and freeing them again. A new
VM flag is used to indicate that these pages should be mapped in only
once, and thus not cached beyond their single use. This prevents
stale data from getting mapped in without the involvement of the file
system, which would be problematic on file systems where file contents
may become outdated at any time. No VM caching means no sharing and
poor performance, but mmap no longer fails on these file systems.
Compared to a libc-based approach, this patch retains the on-demand
nature of mmap. Especially tail(1) is known to map in a large file
area only to use a small portion of it.
All file systems now need to be given permission for the SETCACHEPAGE
and CLEARCACHE calls to VM.
A very basic regression test is added to test74.
Change-Id: I17afc4cb97315b515cad1542521b98f293b6b559
The new functionality aims to save each file system server from having
to implement its own block I/O routines just so that it can serve as a
root file system. The new source file (bio.c) lists the requirements
that file system servers have to fulfill in order to use the routines.
Change-Id: Ia0190fd5c30e8c2097ed8f4b0e3ccde1827e0b92
The file system may not be expecting these upcalls at arbitrary
moments, while they serve only as a performance optimization anyway.
Change-Id: I0748fd1f6c2645ddbb64466093ee36025aac45e0
The minixfs library only ever submits vector elements (and reads) of
the system page size. The test implementation was expecting vector
elements (and reads) of the file system block size. The resulting
mismatch caused I/O to fail in various ways, even though this did not
have an effect on the actual test.
Change-Id: I02f4a3efcd4a32916435d82c7d5798e6b78f0a27
Updating the current block size before flushing the cache, which still
contained blocks with the old block size, resulted in triggering an
assert on position alignment.
Change-Id: I7a83f3d3bc57bafc08aa6c8df64fbf978273bbfd
