Re: [PATCH 1/2] sideband.c: Use xmalloc() instead of variable-sized arrays.

[Junio C Hamano <gitster@pobox.com>]

Nicolas Pitre <nico@cam.org> writes:

> On Tue, 8 Jan 2008, Junio C Hamano wrote:
>
>> Johannes Sixt <j.sixt@viscovery.net> writes:
>> 
>> > From: Johannes Sixt <johannes.sixt@telecom.at>
>> >
>> > How come we got along with this not very portable construct for so long?
>> > Probably because the array sizes were computed from the results of
>> > strlen() of string constants. Anyway, a follow-up patch will make the
>> > lengths really non-constant.
>> >
>> > Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
>> > ---
>> >  sideband.c |   14 ++++++++++++--
>> >  1 files changed, 12 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/sideband.c b/sideband.c
>> > index 756bbc2..513d7b3 100644
>> > --- a/sideband.c
>> > +++ b/sideband.c
>> > @@ -19,7 +19,10 @@ int recv_sideband(const char *me, int in_stream, int out, int err)
>> >  {
>> >  	unsigned pf = strlen(PREFIX);
>> >  	unsigned sf = strlen(SUFFIX);
>> > -	char buf[pf + LARGE_PACKET_MAX + sf + 1];
>> > +	char *buf, *save;
>> > +
>> > +	save = xmalloc(sf);
>> > +	buf = xmalloc(pf + LARGE_PACKET_MAX + sf + 1);
>> 
>> I have to wonder if the malloc() overhead is small enough
>> compared to the network bandwidth to make a two malloc-free
>> pairs per packet a non-issue...
>
> Eeek.  Overhead might be insignificant, but it still doesn't feel right.
>
> What about using alloca() instead?  This is not like if we are doing 
> funky things with the allocated memory anyway.

That's double Eek as I recall AIX is not dead.

How about using a constant large enough slop?  It is not like
PREFIX and SUFFIX are different vastly between calls.