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authorDominique Martinet <asmadeus@codewreck.org>2024-08-08 14:29:38 +0100
committerChristian Brauner <brauner@kernel.org>2024-08-13 13:53:09 +0200
commite3786b29c54cdae3490b07180a54e2461f42144c (patch)
tree02ba9e2224af370d93d92ff6ce6b793ec77aec6d /fs/afs
parent2a0629834cd82f05d424bbc193374f9a43d1f87d (diff)
9p: Fix DIO read through netfs
If a program is watching a file on a 9p mount, it won't see any change in size if the file being exported by the server is changed directly in the source filesystem, presumably because 9p doesn't have change notifications, and because netfs skips the reads if the file is empty. Fix this by attempting to read the full size specified when a DIO read is requested (such as when 9p is operating in unbuffered mode) and dealing with a short read if the EOF was less than the expected read. To make this work, filesystems using netfslib must not set NETFS_SREQ_CLEAR_TAIL if performing a DIO read where that read hit the EOF. I don't want to mandatorily clear this flag in netfslib for DIO because, say, ceph might make a read from an object that is not completely filled, but does not reside at the end of file - and so we need to clear the excess. This can be tested by watching an empty file over 9p within a VM (such as in the ktest framework): while true; do read content; if [ -n "$content" ]; then echo $content; break; fi; done < /host/tmp/foo then writing something into the empty file. The watcher should immediately display the file content and break out of the loop. Without this fix, it remains in the loop indefinitely. Fixes: 80105ed2fd27 ("9p: Use netfslib read/write_iter") Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218916 Signed-off-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/1229195.1723211769@warthog.procyon.org.uk cc: Eric Van Hensbergen <ericvh@kernel.org> cc: Latchesar Ionkov <lucho@ionkov.net> cc: Christian Schoenebeck <linux_oss@crudebyte.com> cc: Marc Dionne <marc.dionne@auristor.com> cc: Ilya Dryomov <idryomov@gmail.com> cc: Steve French <sfrench@samba.org> cc: Paulo Alcantara <pc@manguebit.com> cc: Trond Myklebust <trond.myklebust@hammerspace.com> cc: v9fs@lists.linux.dev cc: linux-afs@lists.infradead.org cc: ceph-devel@vger.kernel.org cc: linux-cifs@vger.kernel.org cc: linux-nfs@vger.kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Dominique Martinet <asmadeus@codewreck.org> Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs/afs')
-rw-r--r--fs/afs/file.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/afs/file.c b/fs/afs/file.c
index c3f0c45ae9a9..ec1be0091fdb 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -242,7 +242,8 @@ static void afs_fetch_data_notify(struct afs_operation *op)
req->error = error;
if (subreq) {
- __set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
+ if (subreq->rreq->origin != NETFS_DIO_READ)
+ __set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
netfs_subreq_terminated(subreq, error ?: req->actual_len, false);
req->subreq = NULL;
} else if (req->done) {