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Provide a flag whereby a filesystem may request that cifs_perform_write()
perform write-through caching. This involves putting pages directly into
writeback rather than dirty and attaching them to a write operation as we
go.
Further, the writes being made are limited to the byte range being written
rather than whole folios being written. This can be used by cifs, for
example, to deal with strict byte-range locking.
This can't be used with content encryption as that may require expansion of
the write RPC beyond the write being made.
This doesn't affect writes via mmap - those are written back in the normal
way; similarly failed writethrough writes are marked dirty and left to
writeback to retry. Another option would be to simply invalidate them, but
the contents can be simultaneously accessed by read() and through mmap.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Implement support for unbuffered writes and direct I/O writes. If the
write is misaligned with respect to the fscrypt block size, then RMW cycles
are performed if necessary. DIO writes are a special case of unbuffered
writes with extra restriction imposed, such as block size alignment
requirements.
Also provide a field that can tell the code to add some extra space onto
the bounce buffer for use by the filesystem in the case of a
content-encrypted file.
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
Implement support for unbuffered and DIO reads in the netfs library,
utilising the existing read helper code to do block splitting and
individual queuing. The code also handles extraction of the destination
buffer from the supplied iterator, allowing async unbuffered reads to take
place.
The read will be split up according to the rsize setting and, if supplied,
the ->clamp_length() method. Note that the next subrequest will be issued
as soon as issue_op returns, without waiting for previous ones to finish.
The network filesystem needs to pause or handle queuing them if it doesn't
want to fire them all at the server simultaneously.
Once all the subrequests have finished, the state will be assessed and the
amount of data to be indicated as having being obtained will be
determined. As the subrequests may finish in any order, if an intermediate
subrequest is short, any further subrequests may be copied into the buffer
and then abandoned.
In the future, this will also take care of doing an unbuffered read from
encrypted content, with the decryption being done by the library.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
netfs_read_folio() needs to handle partially-valid pages that are marked
dirty, but not uptodate in the event that someone tries to read a page was
used to cache data by a streaming write.
In such a case, make netfs_read_folio() set up a bvec iterator that points
to the parts of the folio that need filling and to a sink page for the data
that should be discarded and use that instead of i_pages as the iterator to
be written to.
This requires netfs_rreq_unlock_folios() to convert the page into a normal
dirty uptodate page, getting rid of the partial write record and bumping
the group pointer over to folio->private.
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
Provide a netfs write helper, netfs_perform_write() to buffer data to be
written in the pagecache and mark the modified folios dirty.
It will perform "streaming writes" for folios that aren't currently
resident, if possible, storing data in partially modified folios that are
marked dirty, but not uptodate. It will also tag pages as belonging to
fs-specific write groups if so directed by the filesystem.
This is derived from generic_perform_write(), but doesn't use
->write_begin() and ->write_end(), having that logic rolled in instead.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Dispatch one or more write reqeusts to process a writeback slice, where a
slice is tailored more to logical block divisions within the file (such as
crypto blocks, an object layout or cache granules) than the protocol RPC
maximum capacity.
The dispatch doesn't happen until throttling allows, at which point the
entire writeback slice is processed and queued. A slice may be written to
multiple destinations (one or more servers and the local cache) and the
writes to each destination might be split up along different lines.
The writeback slice holds the required folios pinned. An iov_iter is
provided in netfs_write_request that describes the buffer to be used. This
may be part of the pagecache, may have auxiliary padding pages attached or
may be a bounce buffer resulting from crypto or compression. Consequently,
the filesystem must not twiddle the folio markings directly.
The following API is available to the filesystem:
(1) The ->create_write_requests() method is called to ask the filesystem
to create the requests it needs. This is passed the writeback slice
to be processed.
(2) The filesystem should then call netfs_create_write_request() to create
the requests it needs.
(3) Once a request is initialised, netfs_queue_write_request() can be
called to dispatch it asynchronously, if not completed immediately.
(4) netfs_write_request_completed() should be called to note the
completion of a request.
(5) netfs_get_write_request() and netfs_put_write_request() are provided
to refcount a request. These take constants from the netfs_wreq_trace
enum for logging into ftrace.
(6) The ->free_write_request is method is called to ask the filesystem to
clean up a request.
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
Make the refcounting of netfs_begin_read() easier to use by not eating the
caller's ref on the netfs_io_request it's given. This makes it easier to
use when we need to look in the request struct after.
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
Modify the netfs_io_request struct to act as a point around which writes
can be coordinated. It represents and pins a range of pages that need
writing and a list of regions of dirty data in that range of pages.
If RMW is required, the original data can be downloaded into the bounce
buffer, decrypted if necessary, the modifications made, then the modified
data can be reencrypted/recompressed and sent back to the server.
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
Limit a subrequest to a maximum size and/or a maximum number of contiguous
physical regions. This permits, for instance, an subreq's iterator to be
limited to the number of DMA'able segments that a large RDMA request can
handle.
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
