Re: [patch] __readall() and __readvall() in nscd/nscd_helper.c

[mdm at google dot com]

In case the patch being an attachment is a problem, here it is in the
message:

> Hi all,
>
> When nscd has a sufficiently large reply to a query (for instance a group
> with many members), the entire reply may not yet be ready for reading in
> the client when it first returns from __poll() indicating that the socket
> is ready for reading. The functions __readall() and __readvall() in
> nscd/nscd_helper.c expect that the entire reply can be read immediately,
> since __poll() indicated that the socket was ready, but in reality this is
> not always the case - nscd may need to get scheduled again before more
> data will be available.
>
> The effect of this problem is that when using nscd, calls to functions
> like getgrgid() may fail intermittently when the reply is large. The
> attached patch adds calls to __poll() inside the loops in these two
> functions when errno is EAGAIN to correct the problem.
>
> Mike Mammarella

--- nscd/nscd_helper.c  2006-02-28 21:39:03.000000000 -0800
+++ nscd/nscd_helper.c  2006-09-14 16:29:45.812773000 -0700
@@ -44,6 +44,14 @@
   do
     {
       ret = TEMP_FAILURE_RETRY (__read (fd, buf, n));
+      if (ret < 0 && errno == EAGAIN)
+       {
+         struct pollfd fds[1];
+         fds[0].fd = fd;
+         fds[0].events = POLLIN | POLLERR | POLLHUP;
+         if (__poll (fds, 1, 200) > 0)
+           continue;
+       }
       if (ret <= 0)
        break;
       buf = (char *) buf + ret;
@@ -58,8 +66,10 @@
 __readvall (int fd, const struct iovec *iov, int iovcnt)
 {
   ssize_t ret = TEMP_FAILURE_RETRY (__readv (fd, iov, iovcnt));
-  if (ret <= 0)
+  if (ret <= 0 && errno != EAGAIN)
     return ret;
+  if (ret < 0)
+    ret = 0;

   size_t total = 0;
   for (int i = 0; i < iovcnt; ++i)
@@ -82,6 +92,17 @@
          iovp->iov_base = (char *) iovp->iov_base + r;
          iovp->iov_len -= r;
          r = TEMP_FAILURE_RETRY (__readv (fd, iovp, iovcnt));
+         if (r < 0 && errno == EAGAIN)
+           {
+             struct pollfd fds[1];
+             fds[0].fd = fd;
+             fds[0].events = POLLIN | POLLERR | POLLHUP;
+             if (__poll (fds, 1, 200) > 0)
+               {
+                 r = 0;
+                 continue;
+               }
+           }
          if (r <= 0)
            break;
          ret += r;