Re: [Qemu-devel] [5532] Replace uses of strndup (a GNU extension) with Qemu pstrdup

[andrzej zaborowski]

2008/10/25 Blue Swirl <address@hidden>:
> On 10/25/08, andrzej zaborowski <address@hidden> wrote:
>> 2008/10/25 Blue Swirl <address@hidden>:
>>  > On 10/25/08, andrzej zaborowski <address@hidden> wrote:
>>  >> 2008/10/25 Blue Swirl <address@hidden>:
>>  >>
>>  >> > Revision: 5532
>>  >>  >          
>> http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5532
>>  >>  > Author:   blueswir1
>>  >>  > Date:     2008-10-25 11:23:27 +0000 (Sat, 25 Oct 2008)
>>  >>  >
>>  >>  > Log Message:
>>  >>  > -----------
>>  >>  > Replace uses of strndup (a GNU extension) with Qemu pstrdup
>>  >>  >
>>  >>  > Modified Paths:
>>  >>  > --------------
>>  >>  >    trunk/cutils.c
>>  >>  >    trunk/hw/bt-hci.c
>>  >>  >    trunk/qemu-common.h
>>  >>  >
>>  >>  > Modified: trunk/cutils.c
>>  >>  > ===================================================================
>>  >>  > --- trunk/cutils.c      2008-10-25 11:21:28 UTC (rev 5531)
>>  >>  > +++ trunk/cutils.c      2008-10-25 11:23:27 UTC (rev 5532)
>>  >>  > @@ -50,6 +50,18 @@
>>  >>  >     return buf;
>>  >>  >  }
>>  >>  >
>>  >>  > +/* strdup with a limit */
>>  >>  > +char *pstrdup(const char *str, size_t buf_size)
>>  >>  > +{
>>  >>  > +    size_t len;
>>  >>  > +    char *buf;
>>  >>  > +
>>  >>  > +    len = MIN(buf_size, strlen(str));
>>  >>  > +    buf = qemu_malloc(len);
>>  >>  > +    pstrcpy(buf, len, str);
>>  >>  > +    return buf;
>>  >>  > +}
>>  >>
>>  >>
>>  >> I think here also pstrcpy will only copy up to buf_size - 1 characters
>>  >>  while strndup would copy buf_size chars.
>>  >
>>  > That is actually safer if we always want the strings to be NUL terminated.
>>
>>
>> strndup also always NUL terminates the string so it's just as safe,
>>  the length is just different.
>>
>>
>>  >
>>  > But the allocation length is wrong, it should be MIN(buf_size, 
>> strlen(str) + 1).
>>
>>
>> By my reading of the manual, it should rather be MIN(buf_size, strlen(str)) 
>> + 1.
>
> But then the length could be incorrect: buf_size + 1.

That's what it should be in case lmp_name is 248 chars long.  I think
the confusion is because you called the parameter buf_size while
strndup calls it n (the number of characters.. not buffer size).

Note that you can use memcpy instead of pstrcpy because the length is
known so there's no need for the overhead.

Cheers