Re: [PATCH 2/2] xfs: fix various problems in xfs_atomic_write_cow_iomap_begin

[John Garry <john.g.garry@oracle.com>]

On 04/11/2025 17:18, Darrick J. Wong wrote:
>> Can you point out that code? I wonder if we should be rejecting anything
>> which goes over s_maxbytes for RWF_ATOMIC.
> generic_write_check_limits:
> https://urldefense.com/v3/__https://elixir.bootlin.com/linux/v6.17.7/ 
> source/fs/read_write.c*L1709__;Iw!!ACWV5N9M2RV99hQ!M- 
> J1QmUWrGHUBb6gf9LHN33HxhBfk3rHcNR5z_glUHClffIPQ5UFQ1zmHpsetFGz3_3lHzUrwyAASD_90A$ 
> 
> xfs_file_dio_write_atomic -> xfs_file_write_checks ->
> generic_write_checks -> generic_write_checks_count ->
> generic_write_check_limits

ok, thanks for the pointer.

So should we stop any possible truncation for RWF_ATOMIC, like:

+++ b/fs/xfs/xfs_file.c
@@ -440,6 +440,9 @@ xfs_file_write_checks(
        if (error <= 0)
                return error;

+       if (error != count && iocb->ki_flags & IOCB_ATOMIC)
+               return -EINVAL;
+
        if (iocb->ki_flags & IOCB_NOWAIT) {
                error = break_layout(inode, false);
                if (error == -EWOULDBLOCK)


Note that I do realize that this may be better in generic fs code.

Thanks,
John