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[PATCH v2 6/6] net: tap: Use qemu_close_range() to close fds
From: |
Bin Meng |
Subject: |
[PATCH v2 6/6] net: tap: Use qemu_close_range() to close fds |
Date: |
Fri, 16 Jun 2023 23:27:37 +0800 |
From: Zhangjin Wu <falcon@tinylab.org>
Current codes using a brute-force traversal of all file descriptors
do not scale on a system where the maximum number of file descriptors
is set to a very large value (e.g.: in a Docker container of Manjaro
distribution it is set to 1073741816). QEMU just looks frozen during
start-up.
The close-on-exec flag (O_CLOEXEC) was introduced since Linux kernel
2.6.23, FreeBSD 8.3, OpenBSD 5.0, Solaris 11. While it's true QEMU
doesn't need to manually close the fds for child process as the proper
O_CLOEXEC flag should have been set properly on files with its own
codes, QEMU uses a huge number of 3rd party libraries and we don't
trust them to reliably be using O_CLOEXEC on everything they open.
Modern Linux and BSDs have the close_range() call we can use to do the
job, and on Linux we have one more way to walk through /proc/self/fd
to complete the task efficiently, which is what qemu_close_range() does.
Reported-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Bin Meng <bmeng@tinylab.org>
---
Changes in v2:
- Change to use qemu_close_range() to close fds for child process efficiently
- v1 link:
https://lore.kernel.org/qemu-devel/20230406112041.798585-1-bmeng@tinylab.org/
net/tap.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)
diff --git a/net/tap.c b/net/tap.c
index 1bf085d422..d482fabdff 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -446,13 +446,13 @@ static void launch_script(const char *setup_script, const
char *ifname,
return;
}
if (pid == 0) {
- int open_max = sysconf(_SC_OPEN_MAX), i;
+ unsigned int last_fd = sysconf(_SC_OPEN_MAX) - 1;
+
+ /* skip stdin, stdout and stderr */
+ qemu_close_range(3, fd - 1);
+ /* skip the currently used fd */
+ qemu_close_range(fd + 1, last_fd);
- for (i = 3; i < open_max; i++) {
- if (i != fd) {
- close(i);
- }
- }
parg = args;
*parg++ = (char *)setup_script;
*parg++ = (char *)ifname;
@@ -536,16 +536,15 @@ static int net_bridge_run_helper(const char *helper,
const char *bridge,
return -1;
}
if (pid == 0) {
- int open_max = sysconf(_SC_OPEN_MAX), i;
+ unsigned int last_fd = sysconf(_SC_OPEN_MAX) - 1, fd = sv[1];
char *fd_buf = NULL;
char *br_buf = NULL;
char *helper_cmd = NULL;
- for (i = 3; i < open_max; i++) {
- if (i != sv[1]) {
- close(i);
- }
- }
+ /* skip stdin, stdout and stderr */
+ qemu_close_range(3, fd - 1);
+ /* skip the currently used fd */
+ qemu_close_range(fd + 1, last_fd);
fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]);
--
2.34.1
- [PATCH v2 0/6] net/tap: Fix QEMU frozen issue when the maximum number of file descriptors is very large, Bin Meng, 2023/06/16
- [PATCH v2 1/6] tests/tcg/cris: Fix the coding style, Bin Meng, 2023/06/16
- [PATCH v2 2/6] tests/tcg/cris: Correct the off-by-one error, Bin Meng, 2023/06/16
- [PATCH v2 5/6] util/async-teardown: Use qemu_close_range() to close fds, Bin Meng, 2023/06/16
- [PATCH v2 3/6] util/async-teardown: Fall back to close fds one by one, Bin Meng, 2023/06/16
- [PATCH v2 6/6] net: tap: Use qemu_close_range() to close fds,
Bin Meng <=
- [PATCH v2 4/6] utils/osdep: Introduce qemu_close_range(), Bin Meng, 2023/06/16