afs: Handle better the server returning excess or short data
When an AFS server is given an FS.FetchData{,64} request to read data from
a file, it is permitted by the protocol to return more or less than was
requested. kafs currently relies on the latter behaviour in readpage{,s}
to handle a partial page at the end of the file (we just ask for a whole
page and clear space beyond the short read).
However, we don't handle all cases. Add:
(1) Handle excess data by discarding it rather than aborting. Note that
we use a common static buffer to discard into so that the decryption
algorithm advances the PCBC state.
(2) Handle a short read that affects more than just the last page.
Note that if a read comes up unexpectedly short of long, it's possible that
the server's copy of the file changed - in which case the data version
number will have been incremented and the callback will have been broken -
in which case all the pages currently attached to the inode will be zapped
anyway at some point.
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/afs/file.c b/fs/afs/file.c
index ba7b71f..a38e1c3 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -184,10 +184,13 @@
if (!req)
goto enomem;
+ /* We request a full page. If the page is a partial one at the
+ * end of the file, the server will return a short read and the
+ * unmarshalling code will clear the unfilled space.
+ */
atomic_set(&req->usage, 1);
req->pos = (loff_t)page->index << PAGE_SHIFT;
- req->len = min_t(size_t, i_size_read(inode) - req->pos,
- PAGE_SIZE);
+ req->len = PAGE_SIZE;
req->nr_pages = 1;
req->pages[0] = page;
get_page(page);