Reading from a file that was just extended by a write, but the write had not yet reached the server would return ENODATA as illustrated by this command: $ xfs_io -c 'open -ft test' -c 'w 4096 1000' -c 'r 0 1000' wrote 1000/1000 bytes at offset 4096 1000.000000 bytes, 1 ops; 0.0001 sec (5.610 MiB/sec and 5882.3529 ops/sec) pread: No data available

Fix this case by having netfs assume zeroes when reads from server come short like AFS and CEPH do

Signed-off-by: Dominique Martinet asmadeus@codewreck.org Co-authored-by: David Howells dhowells@redhat.com Cc: stable@vger.kernel.org --- fs/9p/vfs_addr.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c index c72e9f8f5f32..9a10e68c5f30 100644 --- a/fs/9p/vfs_addr.c +++ b/fs/9p/vfs_addr.c @@ -43,6 +43,11 @@ static void v9fs_req_issue_op(struct netfs_read_subrequest *subreq) iov_iter_xarray(&to, READ, &rreq->mapping->i_pages, pos, len);

total = p9_client_read(fid, pos, &to, &err); + + /* if we just extended the file size, any portion not in + * cache won't be on server and is zeroes */ + __set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags); + netfs_subreq_terminated(subreq, err ?: total, false); }