Commit 41da51bc authored by Andreas Gruenbacher's avatar Andreas Gruenbacher
Browse files

fs: Add IOCB_NOIO flag for generic_file_read_iter 



Add an IOCB_NOIO flag that indicates to generic_file_read_iter that it
shouldn't trigger any filesystem I/O for the actual request or for
readahead.  This allows to do tentative reads out of the page cache as
some filesystems allow, and to take the appropriate locks and retry the
reads only if the requested pages are not cached.

Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
parent dcb7fd82

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -315,6 +315,7 @@ enum rw_hint { 
#define IOCB_SYNC		(1 << 5)

#define IOCB_WRITE		(1 << 6)

#define IOCB_NOWAIT		(1 << 7)

#define IOCB_NOIO		(1 << 9)



struct kiocb {

	struct file		*ki_filp;

mm/filemap.c

+21 −2
Original line number Diff line number Diff line
@@ -2028,7 +2028,7 @@ find_page: 


		page = find_get_page(mapping, index);

		if (!page) {

			if (iocb->ki_flags & IOCB_NOWAIT)

			if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))

				goto would_block;

			page_cache_sync_readahead(mapping,

					ra, filp,
@@ -2038,6 +2038,10 @@ find_page: 
				goto no_cached_page;

		}

		if (PageReadahead(page)) {

			if (iocb->ki_flags & IOCB_NOIO) {

				put_page(page);

				goto out;

			}

			page_cache_async_readahead(mapping,

					ra, filp, page,

					index, last_index - index);
@@ -2160,6 +2164,11 @@ page_not_up_to_date_locked: 
		}



readpage:

		if (iocb->ki_flags & IOCB_NOIO) {

			unlock_page(page);

			put_page(page);

			goto would_block;

		}

		/*

		 * A previous I/O error may have been due to temporary

		 * failures, eg. multipath errors.
@@ -2249,9 +2258,19 @@ EXPORT_SYMBOL_GPL(generic_file_buffered_read); 
 *

 * This is the "read_iter()" routine for all filesystems

 * that can use the page cache directly.

 *

 * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall

 * be returned when no data can be read without waiting for I/O requests

 * to complete; it doesn't prevent readahead.

 *

 * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O

 * requests shall be made for the read or for readahead.  When no data

 * can be read, -EAGAIN shall be returned.  When readahead would be

 * triggered, a partial, possibly empty read shall be returned.

 *

 * Return:

 * * number of bytes copied, even for partial reads

 * * negative error code if nothing was read

 * * negative error code (or 0 if IOCB_NOIO) if nothing was read

 */

ssize_t

generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)

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