fuse: handle extent map files in fuse_passthrough_fadvise()

This addresses a collision between the pending backing_file fadvise
patch and the new extent-mapping code for famfs (which falls into the
passthrough bucket.

A file opened with FOPEN_PASSTHROUGH on an extent map backing has no
backing file: fuse_passthrough_open() returns before setting
ff->passthrough and ff->cred.  fuse_file_fadvise() routes every
FOPEN_PASSTHROUGH file to fuse_passthrough_fadvise(), which installed
the NULL ff->cred on the task with override_creds() and then passed the
NULL backing file to vfs_fadvise().  Any posix_fadvise(), readahead()
or madvise(MADV_WILLNEED) on such a file oopsed.  fio triggers it at
file open with its default invalidate and fadvise_hint settings.

Fall back to generic_fadvise() when there is no backing file, as the
other passthrough helpers fall back to their extent map or generic
implementations.  generic_fadvise() already ignores advice on DAX
inodes while keeping the EINVAL and ESPIPE checks.

Reported-by: Aravind Ramesh <arramesh@micron.com>
Fixes: 69f77a06ffad ("fuse: Forward vfs_fadvise to backing_file in passthrough mode")
Tested-by: John Groves <john@groves.net>
Signed-off-by: John Groves <john@groves.net>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

0 files changed, 0 insertions, 0 deletions