Re: [PATCH] cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB2

[Paulo Alcantara]

David Howells <dhowells@xxxxxxxxxx> writes:

> If a DIO read or an unbuffered read request extends beyond the EOF, the
> server will return a short read and a status code indicating that EOF was
> hit, which gets translated to -ENODATA.  Note that the client does not cap
> the request at i_size, but asks for the amount requested in case there's a
> race on the server with a third party.
>
> Now, on the client side, the request will get split into multiple
> subrequests if rsize is smaller than the full request size.  A subrequest
> that starts before or at the EOF and returns short data up to the EOF will
> be correctly handled, with the NETFS_SREQ_HIT_EOF flag being set,
> indicating to netfslib that we can't read more.
>
> If a subrequest, however, starts after the EOF and not at it, HIT_EOF will
> not be flagged, its error will be set to -ENODATA and it will be abandoned.
> This will cause the request as a whole to fail with -ENODATA.
>
> Fix this by setting NETFS_SREQ_HIT_EOF on any subrequest that lies beyond
> the EOF marker.
>
> Fixes: 1da29f2c39b6 ("netfs, cifs: Fix handling of short DIO read")
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Steve French <sfrench@xxxxxxxxx>
> cc: Paulo Alcantara <pc@xxxxxxxxxxxxx>
> cc: Shyam Prasad N <sprasad@xxxxxxxxxxxxx>
> cc: linux-cifs@xxxxxxxxxxxxxxx
> cc: netfs@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx

Reviewed-by: Paulo Alcantara (Red Hat) <pc@xxxxxxxxxxxxx>