Subject: Re: [PATCH] Modify fsck_commit. Replace memcmp by skip_prefix

From: Ashwin Jha <[email-masked]>
Date: Sun, 23 Mar 2014 18:40:55 +0530

Thanks for your comments, Tanay and Eric.

Regarding the [PATCH v2], I will keep this in mind for the subsequent 
patches.

On 03/23/2014 02:10 PM, Eric Sunshine wrote:
> Thanks for the resubmission. Comments below...
>
> On Sat, Mar 22, 2014 at 11:12 AM, Ashwin Jha <[email-masked]> wrote:
>> Subject: [PATCH] Modify fsck_commit. Replace memcmp by skip_prefix
> In his review, Tanay already mentioned indicating a resubmission via
> [PATCH vN]. Additionally, specify the module or function being
> modified, followed by a colon and space. On this project, it is
> customary to forego capitalization in the subject (and only the
> subject). So, you might write:
>
>      Subject: [PATCH v2] fsck_commit: replace memcmp() by skip_prefix()
>
>> Replace memcmp by skip_prefix as it serves the dual
>> purpose of checking the string for a prefix as well
>> as skipping that prefix.
> Good.
>
>> Signed-off-by: Ashwin Jha <[email-masked]>
>> ---
> Tanay mentioned this already: Below the "---" line under your sign-off
> is where you should, as a courtesy to reviewers, explain what changed
> since the previous attempt. Also, provide a link to the previous
> version, like this [1].
>
> [1]: http://git.661346.n2.nabble.com/PATCH-GSoC-Miniproject-15-Rewrite-fsck-c-fsck-commit-td7606180.html
>
>>   fsck.c |   25 ++++++++++++++-----------
>>   1 file changed, 14 insertions(+), 11 deletions(-)
>>
>> diff --git a/fsck.c b/fsck.c
>> index 64bf279..021b3fc 100644
>> --- a/fsck.c
>> +++ b/fsck.c
>> @@ -6,6 +6,7 @@
>>   #include "commit.h"
>>   #include "tag.h"
>>   #include "fsck.h"
>> +#include "git-compat-util.h"
>>
>>   static int fsck_walk_tree(struct tree *tree, fsck_walk_func walk, void *data)
>>   {
>> @@ -284,21 +285,23 @@ static int fsck_ident(char **ident, struct object *obj, fsck_error error_func)
>>
>>   static int fsck_commit(struct commit *commit, fsck_error error_func)
>>   {
>> -       char *buffer = commit->buffer;
>> +       char *next_parent, *buffer = commit->buffer;
> The name 'next_parent' doesn't seem correct. After invoking
> skip_prefix(), this variable will point at the hex representation of
> the parent's SHA1, so a better name might be 'parent_id'.
>
>>          unsigned char tree_sha1[20], sha1[20];
>>          struct commit_graft *graft;
>>          int parents = 0;
>>          int err;
>>
>> -       if (memcmp(buffer, "tree ", 5))
>> +       buffer = (char *)skip_prefix(buffer, "tree ");
> These casts are ugly. It should be possible to get rid of all of them.
> Hint: Does this function modify the memory referenced by 'buffer'?
> (The answer is very slightly involved, though not difficult. A proper
> fix would involve turning this submission into a 2-patch series: one a
> preparatory patch, and the other this patch without the casts.)
Eric, certainly this function does not modify the memory referenced by 
'buffer'.
So, 'buffer' should be declared as a const char *.
But, what about the argument to fsck_ident(). First argument required is 
a char **.
Now, the compiler will correctly give a warning for incorrect argument type.

I have seen the code of fsck_ident(), and it is nowhere modifying the 
memory referenced by
buffer. So, I know that this will not cause any problem. But, still it 
will be a bad practice to do away with
warnings.

And can you explain me a bit about a 2-patch series.

Once again thanks for your help.
>> +       if (buffer == NULL)
>>
>> On this project, it is customary to say !buffer. Ditto for the
>> remaining instances.
>>
>>                  return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
>> -       if (get_sha1_hex(buffer+5, tree_sha1) || buffer[45] != '\n')
>> +       if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')
>>                  return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
>> -       buffer += 46;
>> -       while (!memcmp(buffer, "parent ", 7)) {
>> -               if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n')
>> +       buffer += 41;
>> +       while ((next_parent = (char *)skip_prefix(buffer, "parent ")) != NULL) {
> Likewise, on this project, it is customary to omit the '!= NULL'.
>
>> +               buffer = next_parent;
>> +               if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n')
>>                          return error_func(&commit->object, FSCK_ERROR, "invalid 'parent' line format - bad sha1");
>> -               buffer += 48;
>> +               buffer += 41;
>>                  parents++;
>>          }
>>          graft = lookup_commit_graft(commit->object.sha1);
>> @@ -322,15 +325,15 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
>>                  if (p || parents)
>>                          return error_func(&commit->object, FSCK_ERROR, "parent objects missing");
>>          }
>> -       if (memcmp(buffer, "author ", 7))
>> +       buffer = (char *)skip_prefix(buffer, "author ");
>> +       if (buffer == NULL)
>>                  return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'author' line");
>> -       buffer += 7;
>>          err = fsck_ident(&buffer, &commit->object, error_func);
>>          if (err)
>>                  return err;
>> -       if (memcmp(buffer, "committer ", strlen("committer ")))
>> +       buffer = (char *)skip_prefix(buffer, "committer ");
>> +       if (buffer == NULL)
>>                  return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'committer' line");
>> -       buffer += strlen("committer ");
>>          err = fsck_ident(&buffer, &commit->object, error_func);
>>          if (err)
>>                  return err;
> Other than the minor points mentioned above, the patch looks good. Thanks.
>
>> --
>> 1.7.9.5
Regards,
Ashwin