Re: [PATCH] stream_to_pack: xread does not guarantee to read all requested bytes

On Tue, Aug 20, 2013 at 5:00 PM, Junio C Hamano [off-list ref] wrote:

Johannes Sixt [off-list ref] writes:

quoted

The deflate loop in bulk-checkin::stream_to_pack expects to get all bytes
from a file that it requests to read in a single function call. But it
used xread(), which does not give that guarantee. Replace it by
read_in_full().

Signed-off-by: Johannes Sixt <redacted>
---
 The size is limited to sizeof(ibuf) == 16384 bytes, so that there
 should not be a problem with the unpatched code on any OS in practice.
 Nevertheless, this change seems reasonable from a code hygiene POV.

 bulk-checkin.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bulk-checkin.c b/bulk-checkin.c
index 6b0b6d4..118c625 100644
--- a/bulk-checkin.c
+++ b/bulk-checkin.c

@@ -114,7 +114,7 @@ static int stream_to_pack(struct bulk_checkin_state *state,

              if (size && !s.avail_in) {
                      ssize_t rsize = size < sizeof(ibuf) ? size : sizeof(ibuf);
-                     if (xread(fd, ibuf, rsize) != rsize)
+                     if (read_in_full(fd, ibuf, rsize) != rsize)

This is the kind of thing i was wondering and worried about with the
other "clipped xread/xwrite" patch.  The original of this caller is
obviously wrong.  Thanks for spotting and fixing.

I wonder if there are more like this broken caller or xread and/or
xwrite.

I was actually wondering when it's better to use xread() over
read_in_full() ? Considering that we don't know if xread() will read
the whole buffer or not, would it not be better to always use
read_in_full() ? I guess there is a drawback to this, but I'm not
exactly sure what it is.