It may occasionally be useful to share a listen socket between two
or more tasks with different processing models (blocking and
non-blocking).
This may happen during a software upgrade when an older process
(using blocking I/O) shares the listen socket with a new process
which wants to use non-blocking I/O, but still provides a path for
the old process to fall back to blocking I/O and avoiding poll()
for exclusive wakeup if the upgrade does not work out.
Proposed manpage addtion:
SOCK_DONTWAIT
Enable non-blocking operation on the listen socket for this call only.
Unlike SOCK_NONBLOCK, this does not affect the accepted socket, nor does
it change the file status flag of the listen socket for other calls.
Signed-off-by: Eric Wong <normalperson@xxxxxxxx>
---
RFC since this seems a bit esoteric, and I'm not sure if it'd be
useful to others. I've certainly wished I've had it a few times
along with an opposite SOCK_MUSTWAIT flag to ignore O_NONBLOCK on
a listen socket.
include/linux/net.h | 3 +++
net/socket.c | 10 ++++++++--
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/include/linux/net.h b/include/linux/net.h
index 17d8339..9a71654 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -76,6 +76,9 @@ enum sock_type {
#ifndef SOCK_NONBLOCK
#define SOCK_NONBLOCK O_NONBLOCK
#endif
+#ifndef SOCK_DONTWAIT
+#define SOCK_DONTWAIT MSG_DONTWAIT
+#endif
#endif /* ARCH_HAS_SOCKET_TYPES */
diff --git a/net/socket.c b/net/socket.c
index 245330c..52395df 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1294,6 +1294,7 @@ SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
+ BUILD_BUG_ON(SOCK_DONTWAIT & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK;
if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
@@ -1502,8 +1503,9 @@ SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,
struct file *newfile;
int err, len, newfd, fput_needed;
struct sockaddr_storage address;
+ int f_flags;
- if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
+ if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK | SOCK_DONTWAIT))
return -EINVAL;
if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
@@ -1513,6 +1515,10 @@ SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,
if (!sock)
goto out;
+ f_flags = sock->file->f_flags;
+ if (flags & SOCK_DONTWAIT)
+ f_flags |= O_NONBLOCK;
+
err = -ENFILE;
newsock = sock_alloc();
if (!newsock)
@@ -1545,7 +1551,7 @@ SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,
if (err)
goto out_fd;
- err = sock->ops->accept(sock, newsock, sock->file->f_flags);
+ err = sock->ops->accept(sock, newsock, f_flags);
if (err < 0)
goto out_fd;
--
EW
--
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