From 4e260a8fd740aa0dcecafe79c4f9d3013a21f1ca Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 1 Nov 2022 14:52:47 +0000 Subject: cifs: Implement splice_read to pass down ITER_BVEC not ITER_PIPE Provide cifs_splice_read() to use a bvec rather than an pipe iterator as the latter cannot so easily be split and advanced, which is necessary to pass an iterator down to the bottom levels. Upstream cifs gets around this problem by using iov_iter_get_pages() to prefill the pipe and then passing the list of pages down. This is done by: (1) Bulk-allocate a bunch of pages to carry as much of the requested amount of data as possible, but without overrunning the available slots in the pipe and add them to an ITER_BVEC. (2) Synchronously call ->read_iter() to read into the buffer. (3) Discard any unused pages. (4) Load the remaining pages into the pipe in order and advance the head pointer. Signed-off-by: David Howells cc: Steve French cc: Shyam Prasad N cc: Rohith Surabattula cc: Jeff Layton cc: Al Viro cc: linux-cifs@vger.kernel.org Link: https://lore.kernel.org/r/166732028113.3186319.1793644937097301358.stgit@warthog.procyon.org.uk/ # rfc Signed-off-by: Steve French --- fs/cifs/cifsfs.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'fs/cifs/cifsfs.h') diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h index 63a0ac2b9355..25decebbc478 100644 --- a/fs/cifs/cifsfs.h +++ b/fs/cifs/cifsfs.h @@ -100,6 +100,9 @@ extern ssize_t cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to); extern ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from); extern ssize_t cifs_direct_writev(struct kiocb *iocb, struct iov_iter *from); extern ssize_t cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from); +extern ssize_t cifs_splice_read(struct file *in, loff_t *ppos, + struct pipe_inode_info *pipe, size_t len, + unsigned int flags); extern int cifs_flock(struct file *pfile, int cmd, struct file_lock *plock); extern int cifs_lock(struct file *, int, struct file_lock *); extern int cifs_fsync(struct file *, loff_t, loff_t, int); -- cgit