diff options
| author | Jingbo Xu | 2024-02-26 11:54:35 +0800 |
|---|---|---|
| committer | Miklos Szeredi | 2024-03-06 09:56:34 +0100 |
| commit | e022f6a1c711ab6d76e9e59dce77e2b25df75076 (patch) | |
| tree | 3d807b8cf50b63f63900525ffa97440361493f11 /include/uapi | |
| parent | 5a4d888e9f9beeb5062fbddf789278de5295e9f8 (diff) | |
fuse: add support for explicit export disabling
open_by_handle_at(2) can fail with -ESTALE with a valid handle returned
by a previous name_to_handle_at(2) for evicted fuse inodes, which is
especially common when entry_valid_timeout is 0, e.g. when the fuse
daemon is in "cache=none" mode.
The time sequence is like:
name_to_handle_at(2) # succeed
evict fuse inode
open_by_handle_at(2) # fail
The root cause is that, with 0 entry_valid_timeout, the dput() called in
name_to_handle_at(2) will trigger iput -> evict(), which will send
FUSE_FORGET to the daemon. The following open_by_handle_at(2) will send
a new FUSE_LOOKUP request upon inode cache miss since the previous inode
eviction. Then the fuse daemon may fail the FUSE_LOOKUP request with
-ENOENT as the cached metadata of the requested inode has already been
cleaned up during the previous FUSE_FORGET. The returned -ENOENT is
treated as -ESTALE when open_by_handle_at(2) returns.
This confuses the application somehow, as open_by_handle_at(2) fails
when the previous name_to_handle_at(2) succeeds. The returned errno is
also confusing as the requested file is not deleted and already there.
It is reasonable to fail name_to_handle_at(2) early in this case, after
which the application can fallback to open(2) to access files.
Since this issue typically appears when entry_valid_timeout is 0 which
is configured by the fuse daemon, the fuse daemon is the right person to
explicitly disable the export when required.
Also considering FUSE_EXPORT_SUPPORT actually indicates the support for
lookups of "." and "..", and there are existing fuse daemons supporting
export without FUSE_EXPORT_SUPPORT set, for compatibility, we add a new
INIT flag for such purpose.
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'include/uapi')
| -rw-r--r-- | include/uapi/linux/fuse.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 1162a47b6a42..a86c2cad65ad 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -215,6 +215,7 @@ * 7.40 * - add max_stack_depth to fuse_init_out, add FUSE_PASSTHROUGH init flag * - add backing_id to fuse_open_out, add FOPEN_PASSTHROUGH open flag + * - add FUSE_NO_EXPORT_SUPPORT init flag */ #ifndef _LINUX_FUSE_H @@ -416,6 +417,7 @@ struct fuse_file_lock { * symlink and mknod (single group that matches parent) * FUSE_HAS_EXPIRE_ONLY: kernel supports expiry-only entry invalidation * FUSE_DIRECT_IO_ALLOW_MMAP: allow shared mmap in FOPEN_DIRECT_IO mode. + * FUSE_NO_EXPORT_SUPPORT: explicitly disable export support */ #define FUSE_ASYNC_READ (1 << 0) #define FUSE_POSIX_LOCKS (1 << 1) @@ -456,6 +458,7 @@ struct fuse_file_lock { #define FUSE_HAS_EXPIRE_ONLY (1ULL << 35) #define FUSE_DIRECT_IO_ALLOW_MMAP (1ULL << 36) #define FUSE_PASSTHROUGH (1ULL << 37) +#define FUSE_NO_EXPORT_SUPPORT (1ULL << 38) /* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */ #define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP |