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fuse: add FOPEN_NOFLUSH

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Add flag returned by FUSE_OPEN and FUSE_CREATE requests to avoid flushing
data cache on close.

Different filesystems implement ->flush() is different ways:
 - Most disk filesystems do not implement ->flush() at all
 - Some network filesystem (e.g. nfs) flush local write cache of
   FMODE_WRITE file and send a "flush" command to server
 - Some network filesystem (e.g. cifs) flush local write cache of
   FMODE_WRITE file without sending an additional command to server

FUSE flushes local write cache of ANY file, even non FMODE_WRITE
and sends a "flush" command to server (if server implements it).

The FUSE implementation of ->flush() seems over agressive and
arbitrary and does not make a lot of sense when writeback caching is
disabled.

Instead of deciding on another arbitrary implementation that makes
sense, leave the choice of per-file flush behavior in the hands of
the server.

Link: https://lore.kernel.org/linux-fsdevel/CAJfpegspE8e6aKd47uZtSYX8Y-1e1FWS0VL0DH2Skb9gQP5RJQ@mail.gmail.com/
Suggested-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2021-10-24 16:26:07 +03:00 committed by Miklos Szeredi
parent c6c745b810
commit a390ccb316
2 changed files with 9 additions and 1 deletions
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3
fs/fuse/file.c
View file

@ -476,6 +476,9 @@ static int fuse_flush(struct file *file, fl_owner_t id)
if (fuse_is_bad(inode))
return -EIO;
if (ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache)
return 0;
err = write_inode_now(inode, 1);
if (err)
return err;

7
include/uapi/linux/fuse.h
View file

@ -184,6 +184,9 @@
*
* 7.34
* - add FUSE_SYNCFS
*
* 7.35
* - add FOPEN_NOFLUSH
*/
#ifndef _LINUX_FUSE_H
@ -219,7 +222,7 @@
#define FUSE_KERNEL_VERSION 7
/** Minor version number of this interface */
#define FUSE_KERNEL_MINOR_VERSION 34
#define FUSE_KERNEL_MINOR_VERSION 35
/** The node ID of the root inode */
#define FUSE_ROOT_ID 1
@ -290,12 +293,14 @@ struct fuse_file_lock {
* FOPEN_NONSEEKABLE: the file is not seekable
* FOPEN_CACHE_DIR: allow caching this directory
* FOPEN_STREAM: the file is stream-like (no file position at all)
* FOPEN_NOFLUSH: don't flush data cache on close (unless FUSE_WRITEBACK_CACHE)
*/
#define FOPEN_DIRECT_IO (1 << 0)
#define FOPEN_KEEP_CACHE (1 << 1)
#define FOPEN_NONSEEKABLE (1 << 2)
#define FOPEN_CACHE_DIR (1 << 3)
#define FOPEN_STREAM (1 << 4)
#define FOPEN_NOFLUSH (1 << 5)
/**
* INIT request/reply flags