Re: [PATCH] fs/9p/xattr.c: catch the error of p9_client_clunk when setting xattr failed

piaojun
2018-07-25T03:59:00Z

Hi Dominique,

On 2018/7/25 11:32, Dominique Martinet wrote:
> piaojun wrote on Wed, Jul 25, 2018:
>> In my testing, v9fs_fid_xattr_set will return successfully even if the
>> backend ext4 filesystem has no space to store xattr key-value. That will
>> cause inconsistent behavior between front end and back end. The reason is
>> that lsetxattr will be triggered by p9_client_clunk, and unfortunately we
>> did not catch the error. This patch will catch the error to notify upper
>> caller.
>>
>> p9_client_clunk (in 9p)
>> p9_client_rpc(clnt, P9_TCLUNK, "d", fid->fid);
>> v9fs_clunk (in qemu)
>> put_fid
>> free_fid
>> v9fs_xattr_fid_clunk
>> v9fs_co_lsetxattr
>> s->ops->lsetxattr
>> ext4_xattr_user_set (in host ext4 filesystem)
>>
>> Signed-off-by: Jun Piao <piaojun@huawei.com>
>
> Good catch!
>
> LGTM on its own but see comment below for further error checking.
> Please let me know if you want to do this in a v2 or submit a separate
> patch altogether, I can pick this one up as it is.
>
>> ---
>> fs/9p/xattr.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/9p/xattr.c b/fs/9p/xattr.c
>> index f329eee..352abc3 100644
>> --- a/fs/9p/xattr.c
>> +++ b/fs/9p/xattr.c
>> @@ -105,7 +105,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
>> {
>> struct kvec kvec = {.iov_base = (void *)value, .iov_len = value_len};
>> struct iov_iter from;
>> - int retval;
>> + int retval, err;
>>
>> iov_iter_kvec(&from, WRITE | ITER_KVEC, &kvec, 1, value_len);
>>
>> @@ -126,7 +126,9 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
>> retval);
>> else
>> p9_client_write(fid, 0, &from, &retval);
>
> I'm not sure what to do about this but it's also possible for
> p9_client_write to not write the full length without setting and error.
>
> We should probably compare the return value of p9_client_write and
> value_len to detect short writes and return an error in this case.
>
It looks like we could identify short writes error from the *err. If no
error case breaks the while loop, the total equal to the whole data len.

Thanks,
Jun

>> - p9_client_clunk(fid);
>> + err = p9_client_clunk(fid);
>> + if (!retval && err)
>> + retval = err;
>> return retval;
>> }
>>
>> --
> .
>