Re: [PATCH] upload-pack: use buffered I/O to talk to rev-list

["René Scharfe" <l.s.r@web.de>]

Am 02.08.20 um 18:03 schrieb Chris Torek:
> One suggestion here:
>
> On Sun, Aug 2, 2020 at 7:41 AM René Scharfe <l.s.r@web.de> wrote:
>> Like f0bca72dc77 (send-pack: use buffered I/O to talk to pack-objects,
>> 2016-06-08), significantly reduce the number of system calls and
>> simplify the code for sending object IDs to rev-list by using stdio's
>> buffering and handling errors after the loops.
>>
>> Signed-off-by: René Scharfe <l.s.r@web.de>
>> ---
>>  upload-pack.c | 21 +++++++--------------
>>  1 file changed, 7 insertions(+), 14 deletions(-)
>>
>> diff --git a/upload-pack.c b/upload-pack.c
>> index 86737410709..9f616c2c6a6 100644
>> --- a/upload-pack.c
>> +++ b/upload-pack.c
>
> [snip]
>
>> @@ -640,12 +636,11 @@ static int do_reachable_revlist(struct child_process *cmd,
>>                 }
>>                 if (reachable && o->type == OBJ_COMMIT)
>>                         o->flags |= TMP_MARK;
>> -               memcpy(namebuf, oid_to_hex(&o->oid), hexsz);
>> -               if (write_in_full(cmd->in, namebuf, hexsz + 1) < 0)
>> -                       goto error;
>> +               fprintf(cmd_in, "%s\n", oid_to_hex(&o->oid));
>
> The fprintf() call here *can* return an error, e.g., if the
> connection has died.  If it does, it should set things up so that
> a later ferror(cmd_in) returns true.
>
>>         }
>> -       close(cmd->in);
>>         cmd->in = -1;
>> +       if (fclose(cmd_in))
>> +               goto error;
>
> The fclose() call doesn't necessarily check ferror().  (The
> FreeBSD stdio in particular definitely does not.)  It might
> be better to use:
>
>     failure = ferror(cmd_in);
>     failure |= fclose(cmd_in);
>     if (failure) ...
>
> here, or similar.  (The temporary variable is not needed,
> but someone might assume `if (ferror(fp) | fclose(fp))` is
> a typo for `if (ferror(fp) || fclose(fp))`.)

Thanks, didn't know that.  That's awful.  So the sentence "The fclose()
and fdclose() functions may also fail and set errno for any of the
errors specified for fflush(3)." from the FreeBSD manpage for fclose(3)
actually means that while it will flush, it is free to ignore any
flush errors?

Or do you mean that fflush() can succeed on a stream that has its error
indicator set?

In any case, we'd then better add a function that flushes the buffer,
closes the stream and reports errors in its return code and errno --
i.e. a sane fclose().

René