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virtiofsd: Add basic support for FUSE_SYNCFS request

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Honor the expected behavior of syncfs() to synchronously flush all data
and metadata to disk on linux systems.

If virtiofsd is started with '-o announce_submounts', the client is
expected to send a FUSE_SYNCFS request for each individual submount.
In this case, we just create a new file descriptor on the submount
inode with lo_inode_open(), call syncfs() on it and close it. The
intermediary file is needed because O_PATH descriptors aren't
backed by an actual file and syncfs() would fail with EBADF.

If virtiofsd is started without '-o announce_submounts' or if the
client doesn't have the FUSE_CAP_SUBMOUNTS capability, the client
only sends a single FUSE_SYNCFS request for the root inode. The
server would thus need to track submounts internally and call
syncfs() on each of them. This will be implemented later.

Note that syncfs() might suffer from a time penalty if the submounts
are being hammered by some unrelated workload on the host. The only
solution to prevent that is to avoid shared mounts.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20220215181529.164070-2-groug@kaod.org>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Greg Kurz 2022-02-15 19:15:29 +01:00 • committed by Dr. David Alan Gilbert
parent 963061dc11
commit 45b04ef48d
4 changed files with 69 additions and 0 deletions
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11
tools/virtiofsd/fuse_lowlevel.c
View file

@ -1967,6 +1967,16 @@ static void do_lseek(fuse_req_t req, fuse_ino_t nodeid,
}
}
static void do_syncfs(fuse_req_t req, fuse_ino_t nodeid,
struct fuse_mbuf_iter *iter)
{
if (req->se->op.syncfs) {
req->se->op.syncfs(req, nodeid);
} else {
fuse_reply_err(req, ENOSYS);
}
}
static void do_init(fuse_req_t req, fuse_ino_t nodeid,
struct fuse_mbuf_iter *iter)
{
@ -2399,6 +2409,7 @@ static struct {
[FUSE_RENAME2] = { do_rename2, "RENAME2" },
[FUSE_COPY_FILE_RANGE] = { do_copy_file_range, "COPY_FILE_RANGE" },
[FUSE_LSEEK] = { do_lseek, "LSEEK" },
[FUSE_SYNCFS] = { do_syncfs, "SYNCFS" },
};
#define FUSE_MAXOP (sizeof(fuse_ll_ops) / sizeof(fuse_ll_ops[0]))