There are cases when the filesystem will be passed the buffer from a single
read or write call, namely:
1) in 'direct-io' mode (not O_DIRECT), read/write requests don't go
through the page cache, but go directly to the userspace fs
2) currently buffered writes are done with single page requests, but
if Nick's ->perform_write() patch goes it, it will be possible to
do larger write requests. But only if the original write() was
also bigger than a page.
In these cases the filesystem might want to give a hint to the app
about the optimal I/O size.
Allow the userspace filesystem to supply a blksize value to be returned by
stat() and friends. If the field is zero, it defaults to the old
PAGE_CACHE_SIZE value.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
0e9663ee45