[Libguestfs] [PATCH 1/2] ext2: tweak the error returned message of resize2fs-M(BZ755729)

[Jim Meyering]

Richard W.M. Jones wrote:
> On Fri, Jan 13, 2012 at 02:27:49PM +0800, Wanlong Gao wrote:
>> Tweak the error message "e2fsck -f" and "e2fsck -fy" to
>> "e2fsck-f" and "e2fsck-fy".
>>
>> Signed-off-by: Wanlong Gao <gaowanlong at cn.fujitsu.com>
>> ---
>>  daemon/ext2.c |   20 ++++++++++++++++++--
>>  1 files changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/daemon/ext2.c b/daemon/ext2.c
>> index 79fd354..9fe938e 100644
>> --- a/daemon/ext2.c
>> +++ b/daemon/ext2.c
>> @@ -277,9 +277,25 @@ do_resize2fs_M (const char *device)
>>    if (e2prog (prog) == -1)
>>      return -1;
>>
>> -  r = command (NULL, &err, prog, "-M" , device, NULL);
>> +  r = command (NULL, &err, prog, "-M", device, NULL);
>>    if (r == -1) {
>> -    reply_with_error ("%s", err);
>> +    int i = 0;
>> +    int len = strlen (err);
>
> Use 'size_t' (instead of 'int') for the return value of strlen.
>
> What is 'i' used for?
>
>> +    char *err_wrap = malloc (len + 1);
>> +    if (!err_wrap)
>> +      goto err_out;
>
> You need to call 'reply_with_error' or 'reply_with_perror' exactly
> once on each error path.  So here you'd need to call
>   reply_with_perror ("malloc");
> before the 'goto'.
>
>> +    char *p = strstr (err, "e2fsck -f");
>> +    if (p) {
>> +      strncpy (err_wrap, err, p - err);
>
> Isn't it better to use memcpy here?  AFAIK using strncpy is almost
> always wrong.  (Jim?)

I would.  The fact that strncpy does not always NUL-terminate
makes it hard to use correctly.  Better to avoid it in general.

>> +      err_wrap[p - err] = '\0';
>> +      sprintf(err_wrap + (p - err), "%s%s", "e2fsck-f", p + 9);

Also, as a general rule, it is easier to code and maintain
uses of asprintf than separate malloc+sprintf.
You can depend on asprintf, since it is provided by gnulib, if needed.

And, technically sprintf can fail (with glibc, it may even invoke malloc!),
so you should handle failure.