Re: pread() over NFS (again) [1.5.5.4]

From: Shawn O. Pearce <spearce@spearce.org>
Date: Jun 26, 2008, 20:46 UTC
Message-ID: <20080626204606.GX11793@spearce.org>
In-Reply-To: <6F25C1B4-85DE-4559-9471-BCD453FEB174@gmail.com>

Christian Holtje <docwhat@gmail.com> wrote:

> I have read all the threads on git having trouble with pread() and I  
> didn't see anything to help.

...

Show 7 quoted lines

>   Receiving objects: 100% (253/253), 5.27 MiB | 9136 KiB/s, done.
>   fatal: cannot pread pack file: No such file or directory
>   fatal: index-pack failed
> 
> The end of the strace looks like so:
> pread(3, "", 205, 1373)                 = 0
> write(2, "fatal: cannot pread pack file: N"..., 57) = 57

Hmmph. So pread for a length of 205 can return 0 on NFS? Is this a transient error? If so, perhaps a patch like this might help:

diff --git a/index-pack.c b/index-pack.c
index 5ac91ba..737f757 100644
--- a/index-pack.c
+++ b/index-pack.c
@@ -309,14 +309,19 @@ static void *get_data_from_pack(struct object_entry *obj)
 	unsigned char *src, *data;
 	z_stream stream;
 	int st;
+	int attempts = 0;
 
 	src = xmalloc(len);
 	data = src;
 	do {
 		ssize_t n = pread(pack_fd, data + rdy, len - rdy, from + rdy);
-		if (n <= 0)
+		if (n <= 0) {
+			if (n == 0 && ++attempts < 10)
+				continue;
 			die("cannot pread pack file: %s", strerror(errno));
+		}
 		rdy += n;
+		attempts = 0;
 	} while (rdy < len);
 	data = xmalloc(obj->size);
 	memset(&stream, 0, sizeof(stream));


The file shouldn't be short unless someone truncated it, or there
is a bug in index-pack.  Neither is very likely, but I don't think
we would want to retry pread'ing the same block forever.

-- 
Shawn.