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Borrow NFS's direct-vs-buffered I/O locking into netfslib. Similar code is
also used in ceph.
Modify it to have the correct checker annotations for i_rwsem lock
acquisition/release and to return -ERESTARTSYS if waits are interrupted.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Move the resource pinning-for-writeback from fscache code to netfslib code.
This is used to keep a cache backing object pinned whilst we have dirty
pages on the netfs inode in the pagecache such that VM writeback will be
able to reach it.
Whilst we're at it, switch the parameters of netfs_unpin_writeback() to
match ->write_inode() so that it can be used for that directly.
Note that this mechanism could be more generically useful than that for
network filesystems. Quite often they have to keep around other resources
(e.g. authentication tokens or network connections) until the writeback is
complete.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
There's a problem with dependencies between netfslib and fscache as each
wants to access some functions of the other. Deal with this by moving
fs/fscache/* into fs/netfs/ and renaming those files to begin with
"fscache-".
For the moment, the moved files are changed as little as possible and an
fscache module is still built. A subsequent patch will integrate them.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Christian Brauner <christian@brauner.io>
cc: linux-fsdevel@vger.kernel.org
cc: linux-cachefs@redhat.com
Add a function to extract the pages from a user-space supplied iterator
(UBUF- or IOVEC-type) into a BVEC-type iterator, retaining the pages by
getting a pin on them (as FOLL_PIN) as we go.
This is useful in three situations:
(1) A userspace thread may have a sibling that unmaps or remaps the
process's VM during the operation, changing the assignment of the
pages and potentially causing an error. Retaining the pages keeps
some pages around, even if this occurs; futher, we find out at the
point of extraction if EFAULT is going to be incurred.
(2) Pages might get swapped out/discarded if not retained, so we want to
retain them to avoid the reload causing a deadlock due to a DIO
from/to an mmapped region on the same file.
(3) The iterator may get passed to sendmsg() by the filesystem. If a
fault occurs, we may get a short write to a TCP stream that's then
tricky to recover from.
We don't deal with other types of iterator here, leaving it to other
mechanisms to retain the pages (eg. PG_locked, PG_writeback and the pipe
lock).
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: linux-cachefs@redhat.com
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
