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Cygwin: AF_UNIX: sendmsg: wait for a pipe instance in the datagram case

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When trying to connect to the pipe created by the remote socket,
open_pipe might fail if there are no pipe instances available.  This
can happen if there has been a previous connection to the same pipe.
The server end of the pipe won't be available again until it
disconnects the previous connection.  (This is done in recvmsg.)

Introduce and use a new method fhandler_socket_unix::wait_open_pipe
that waits (in the blocking case) for an instance to become available.
This commit is contained in:
Ken Brown 2021-04-01 11:06:24 -04:00
parent 451ec9bb13
commit 24ac223828
2 changed files with 87 additions and 1 deletions
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1
winsup/cygwin/fhandler.h
View File

@ -1186,6 +1186,7 @@ class fhandler_socket_unix : public fhandler_socket
HANDLE create_pipe (bool single_instance);
HANDLE create_pipe_instance ();
NTSTATUS open_pipe (HANDLE &ph, PUNICODE_STRING pipe_name);
int wait_open_pipe (HANDLE &ph, PUNICODE_STRING pipe_name);
void xchg_sock_info ();
int wait_pipe (PUNICODE_STRING pipe_name);
int connect_pipe (PUNICODE_STRING pipe_name);

87
winsup/cygwin/fhandler_socket_unix.cc
View File

@ -1479,6 +1479,81 @@ out:
return error;
}
/* A variant of wait_pipe_thread, called by sendmsg in datagram case.
Wait for a pipe instance to become available and connect to it. */
int
fhandler_socket_unix::wait_open_pipe (HANDLE &ph, PUNICODE_STRING pipe_name)
{
HANDLE npfsh;
HANDLE evt;
NTSTATUS status;
IO_STATUS_BLOCK io;
ULONG pwbuf_size;
PFILE_PIPE_WAIT_FOR_BUFFER pwbuf;
int ret = -1;
status = npfs_handle (npfsh);
if (!NT_SUCCESS (status))
{
__seterrno_from_nt_status (status);
goto out;
}
if (!(evt = create_event ()))
goto out;
pwbuf_size = offsetof (FILE_PIPE_WAIT_FOR_BUFFER, Name) + pipe_name->Length;
pwbuf = (PFILE_PIPE_WAIT_FOR_BUFFER) alloca (pwbuf_size);
pwbuf->NameLength = pipe_name->Length;
pwbuf->TimeoutSpecified = FALSE;
memcpy (pwbuf->Name, pipe_name->Buffer, pipe_name->Length);
retry:
status = NtFsControlFile (npfsh, evt, NULL, NULL, &io, FSCTL_PIPE_WAIT,
pwbuf, pwbuf_size, NULL, 0);
if (status == STATUS_PENDING)
{
switch (cygwait (evt, cw_infinite, cw_cancel | cw_sig_eintr))
{
case WAIT_OBJECT_0:
status = io.Status;
break;
case WAIT_CANCELED:
pthread::static_cancel_self ();
/*NOTREACHED*/
case WAIT_SIGNALED:
set_errno (EINTR);
break;
default:
break;
}
}
switch (status)
{
case STATUS_SUCCESS:
status = open_pipe (ph, pipe_name);
if (NT_SUCCESS (status))
ret = 0;
else if (STATUS_PIPE_NO_INSTANCE_AVAILABLE (status))
/* Someone else grabbed the pipe instance. */
goto retry;
else
__seterrno_from_nt_status (status);
break;
case STATUS_OBJECT_NAME_NOT_FOUND:
set_errno (EADDRNOTAVAIL);
break;
case STATUS_INSUFFICIENT_RESOURCES:
set_errno (ENOBUFS);
break;
case STATUS_INVALID_DEVICE_REQUEST:
default:
set_errno (EIO);
break;
}
out:
if (evt)
NtClose (evt);
return ret;
}
int
fhandler_socket_unix::socket (int af, int type, int protocol, int flags)
{
@ -3106,7 +3181,17 @@ fhandler_socket_unix::sendmsg (const struct msghdr *msg, int flags)
__leave;
}
status = open_pipe (ph, &pipe_name);
if (!NT_SUCCESS (status))
if (STATUS_PIPE_NO_INSTANCE_AVAILABLE (status))
{
if (is_nonblocking () || flags & MSG_DONTWAIT)
{
set_errno (EAGAIN);
__leave;
}
if (wait_open_pipe (ph, &pipe_name) < 0)
__leave;
}
else if (!NT_SUCCESS (status))
{
__seterrno_from_nt_status (status);
__leave;