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

From: Chris Torek <chris.torek@gmail.com>
Date: Aug 2, 2020, 16:03 UTC
Message-ID: <CAPx1GvdJ-4Yyf7Vm1OdhaW2TZp77HOfGxoGw0R2fKfEuHQkqOg@mail.gmail.com>
In-Reply-To: <6722ade6-971e-7ecc-e8f0-7f595ca0b0ff@web.de>

One suggestion here:

On Sun, Aug 2, 2020 at 7:41 AM René Scharfe <l.s.r@web.de> wrote:

Show 14 quoted lines

> 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]

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> @@ -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.

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>         }
> -       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))`.)

(Note: my sample isn't properly indented as gmail does not let me insert tabs easily)

Chris