RE: [PATCH] cifs: only write 64kb at a time when fallocating a small region of a file

["Namjae Jeon" <namjae.jeon@samsung.com>]

Hi Ronnie,

> We only allow sending single credit writes through the SMB2_write() synchronous api so split this into
> smaller chunks.
> 
> Fixes: 966a3cb7c7db ("cifs: improve fallocate emulation")
> 
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>  fs/cifs/smb2ops.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index ba3c58e1f725..7fefa100887b 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -3617,7 +3617,7 @@ static int smb3_simple_fallocate_write_range(unsigned int xid,
>                                              char *buf)  {
>         struct cifs_io_parms io_parms = {0};
> -       int nbytes;
> +       int rc, nbytes;
>         struct kvec iov[2];
> 
>         io_parms.netfid = cfile->fid.netfid; @@ -3625,13 +3625,25 @@ static int
> smb3_simple_fallocate_write_range(unsigned int xid,
>         io_parms.tcon = tcon;
>         io_parms.persistent_fid = cfile->fid.persistent_fid;
>         io_parms.volatile_fid = cfile->fid.volatile_fid;
> -       io_parms.offset = off;
> -       io_parms.length = len;
> 
> -       /* iov[0] is reserved for smb header */
> -       iov[1].iov_base = buf;
> -       iov[1].iov_len = io_parms.length;
> -       return SMB2_write(xid, &io_parms, &nbytes, iov, 1);
> +       while (len) {
> +               io_parms.offset = off;
> +               io_parms.length = len;
> +               if (io_parms.length > 65536)
> +                       io_parms.length = 65536;
Minor nit, We can probably use a defined macro, SMB2_MAX_BUFFER_SIZE.

> +               /* iov[0] is reserved for smb header */
> +               iov[1].iov_base = buf;
> +               iov[1].iov_len = io_parms.length;
> +               rc = SMB2_write(xid, &io_parms, &nbytes, iov, 1);
> +               if (rc)
> +                       break;
> +               if (nbytes > len)
> +                       return -EINVAL;
> +               buf += nbytes;
> +               off += nbytes;
> +               len -= nbytes;
> +       }
> +       return rc;
>  }
> 
>  static int smb3_simple_fallocate_range(unsigned int xid, @@ -3655,11 +3667,6 @@ static int
> smb3_simple_fallocate_range(unsigned int xid,
>                         (char **)&out_data, &out_data_len);
>         if (rc)
>                 goto out;
> -       /*
> -        * It is already all allocated
> -        */
> -       if (out_data_len == 0)
> -               goto out;
Is there any reason to remove this code ?
Because xfstests generic/071 test failed against ksmbd without this code.

generic/071 files ... - output mismatch (see /home/linkinjeon/xfstests-ksmbd/results//generic/071.out.bad)
    --- tests/generic/071.out   2020-02-05 09:07:30.000000000 +0900
    +++ /home/linkinjeon/xfstests/xfstests-ksmbd/results//generic/071.out.bad 2021-07-21 15:32:18.001170684 +0900
    @@ -6,4 +6,4 @@
     *
     1000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     *
    -2000000
    +4000000
    ...
    (Run 'diff -u /home/linkinjeon/xfstests-ksmbd/tests/generic/071.out /home/linkinjeon/xfstests-ksmbd/results//generic/071.out.bad'  to see the entire diff)
Ran: generic/071
Failures: generic/071
Failed 1 of 1 tests

Thanks!
> 
>         buf = kzalloc(1024 * 1024, GFP_KERNEL);
>         if (buf == NULL) {
> --
> 2.30.2