* [PATCH 1/1] Cygwin: AF_INET and AF_LOCAL: recv_internal: fix MSG_WAITALL support
2020-10-12 18:02 [PATCH 0/1] Fix MSG_WAITALL support Ken Brown
@ 2020-10-12 18:02 ` Ken Brown
2020-10-12 18:43 ` [PATCH 0/1] Fix " Ken Brown
2020-10-22 19:26 ` Ken Brown
2 siblings, 0 replies; 5+ messages in thread
From: Ken Brown @ 2020-10-12 18:02 UTC (permalink / raw)
To: cygwin-patches
If MSG_WAITALL is set, recv_internal calls WSARecv or WSARecvFrom in a
loop, in an effort to fill all the scatter-gather buffers. The test
for whether all the buffers are full was previously incorrect.
---
winsup/cygwin/fhandler_socket_inet.cc | 2 +-
winsup/cygwin/fhandler_socket_local.cc | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/winsup/cygwin/fhandler_socket_inet.cc b/winsup/cygwin/fhandler_socket_inet.cc
index 71e92e341..bc08d3cf1 100644
--- a/winsup/cygwin/fhandler_socket_inet.cc
+++ b/winsup/cygwin/fhandler_socket_inet.cc
@@ -1208,7 +1208,7 @@ fhandler_socket_inet::recv_internal (LPWSAMSG wsamsg, bool use_recvmsg)
--wsacnt;
}
}
- if (!wret)
+ if (!wsacnt)
break;
}
else if (WSAGetLastError () != WSAEWOULDBLOCK)
diff --git a/winsup/cygwin/fhandler_socket_local.cc b/winsup/cygwin/fhandler_socket_local.cc
index 8bfba225a..c94bf828f 100644
--- a/winsup/cygwin/fhandler_socket_local.cc
+++ b/winsup/cygwin/fhandler_socket_local.cc
@@ -1212,7 +1212,7 @@ fhandler_socket_local::recv_internal (LPWSAMSG wsamsg, bool use_recvmsg)
--wsacnt;
}
}
- if (!wret)
+ if (!wsacnt)
break;
}
else if (WSAGetLastError () != WSAEWOULDBLOCK)
--
2.28.0
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH 0/1] Fix MSG_WAITALL support
2020-10-12 18:02 [PATCH 0/1] Fix MSG_WAITALL support Ken Brown
2020-10-12 18:02 ` [PATCH 1/1] Cygwin: AF_INET and AF_LOCAL: recv_internal: fix " Ken Brown
@ 2020-10-12 18:43 ` Ken Brown
2020-10-22 19:26 ` Ken Brown
2 siblings, 0 replies; 5+ messages in thread
From: Ken Brown @ 2020-10-12 18:43 UTC (permalink / raw)
To: cygwin-patches
[-- Attachment #1: Type: text/plain, Size: 1695 bytes --]
On 10/12/2020 2:02 PM, Ken Brown via Cygwin-patches wrote:
> It looks to me like there's been a bug in the MSG_WAITALL support for
> AF_INET and AF_LOCAL sockets ever since that support was first
> introduced 13 years ago in commit 023a2fa7. If I'm right, MSG_WAITALL
> has never worked.
>
> This patch fixes it. I'll push it in a few days if no one sees
> anything wrong with it.
>
> In a followup email I'll show how I tested it.
Attached are slight variants of the server/client programs from Section 57.2 of
Kerrisk's book, "The Linux Programming Interface". The only essential
difference is that I've changed the server program to (a) use a small buffer
(size 10 instead of 100) and (b) use 'recv' with the MSG_WAITALL flag instead of
'read'. The 'recv' call shouldn't return until it reads 10 bytes.
To test, run waitall_sv in one terminal and waitall_cl in a second. Type
something in the second terminal (followed by RET), and it should be echoed in
the first. But because of the MSG_WAITALL flag, the echoing shouldn't occur
until 10 bytes have been written. For example, if I type "abcd<RET>" in the
second terminal and then do it again, I should see the following:
# Terminal 2:
$ ./waitall_cl
abcd
abcd
# Terminal 1:
$ ./waitall_sv
abcd
abcd
Here the echoing in Terminal 1 shouldn't occur until I've typed both "abcd"
lines in Terminal 2.
[Note that there is a newline character after each "abcd", so "abcd<RET>" is 5
bytes long, and the two lines together are 10 bytes long.]
Before I apply my patch, each line typed in Terminal 2 is immediately echoed in
Terminal 1. After I apply the patch, the echoing doesn't occur until I've typed
both lines.
Ken
[-- Attachment #2: waitall_sv.c --]
[-- Type: text/plain, Size: 1461 bytes --]
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/un.h>
#include <sys/socket.h>
#define SV_SOCK_PATH "/tmp/waitall"
#define BUF_SIZE 10
#define BACKLOG 5
int
main ()
{
struct sockaddr_un addr;
int sfd, cfd;
ssize_t nread;
char buf[BUF_SIZE];
if ((sfd = socket (AF_UNIX, SOCK_STREAM, 0)) < 0)
{
perror ("socket");
exit (1);
}
if (remove (SV_SOCK_PATH) < 0 && errno != ENOENT)
{
perror ("remove");
exit (1);
}
memset (&addr, 0, sizeof (struct sockaddr_un));
addr.sun_family = AF_UNIX;
strncpy (addr.sun_path, SV_SOCK_PATH, sizeof (addr.sun_path) - 1);
if (bind (sfd, (struct sockaddr *) &addr, sizeof (struct sockaddr_un)) < 0)
{
perror ("bind");
exit (1);
}
if (listen (sfd, BACKLOG) < 0)
{
perror ("listen");
exit (1);
}
while (1)
{
cfd = accept (sfd, NULL, NULL);
if (cfd < 0)
{
perror ("accept");
exit (1);
}
/* Transfer data from connected socket to stdout until EOF. */
while ((nread = recv (cfd, buf, BUF_SIZE, MSG_WAITALL)) > 0)
if (write (STDOUT_FILENO, buf, nread) != nread)
{
perror ("partial/failed write");
exit (1);
}
if (nread < 0)
{
perror ("read");
exit (1);
}
if (close (cfd) < 0)
{
perror ("close");
exit (1);
}
}
}
[-- Attachment #3: waitall_cl.c --]
[-- Type: text/plain, Size: 944 bytes --]
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/un.h>
#include <sys/socket.h>
#define SV_SOCK_PATH "/tmp/waitall"
#define BUF_SIZE 100
int
main ()
{
struct sockaddr_un addr;
int sfd;
ssize_t nread;
char buf[BUF_SIZE];
if ((sfd = socket (AF_UNIX, SOCK_STREAM, 0)) < 0)
{
perror ("socket");
exit (1);
}
memset (&addr, 0, sizeof(struct sockaddr_un));
addr.sun_family = AF_UNIX;
strncpy (addr.sun_path, SV_SOCK_PATH, sizeof(addr.sun_path) - 1);
if (connect (sfd, (struct sockaddr *) &addr,
sizeof (struct sockaddr_un)) < 0)
{
perror ("connect");
exit (1);
}
/* Copy stdin to socket. */
while ((nread = read (STDIN_FILENO, buf, BUF_SIZE)) > 0)
if (write (sfd, buf, nread) != nread)
{
perror ("partial/failed write");
exit (1);
}
if (nread < 0)
{
perror ("read");
exit (1);
}
}
^ permalink raw reply [flat|nested] 5+ messages in thread