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block: enable RWF_DONTCACHE for block devices

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Block device buffered reads and writes already pass through
filemap_read() and iomap_file_buffered_write() respectively, both of
which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
by setting FOP_DONTCACHE in def_blk_fops.

For CONFIG_BUFFER_HEAD=y, writeback goes through buffer_head's
__bh_submit() which sets BIO_COMPLETE_IN_TASK on dropbehind folios. For
CONFIG_BUFFER_HEAD=n, writeback goes through iomap which handles it via
BIO_COMPLETE_IN_TASK on the ioend bio.

This support is useful for databases that operate on raw block devices,
among other userspace applications.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260730-blk-dontcache-v7-5-3e8e6850068d@columbia.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tal Zussman 2026-07-30 02:57:55 -04:00 committed by Jens Axboe
parent a2c924c240
commit 8b5ffb43ae
1 changed files with 1 additions and 1 deletions
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2
block/fops.c
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@ -943,7 +943,7 @@ const struct file_operations def_blk_fops = {
.splice_write = iter_file_splice_write,
.fallocate = blkdev_fallocate,
.uring_cmd = blkdev_uring_cmd,
.fop_flags = FOP_BUFFER_RASYNC,
.fop_flags = FOP_BUFFER_RASYNC | FOP_DONTCACHE,
};
static __init int blkdev_init(void)