[Qemu-devel] [PATCH] Avoiding extra iterations while closing file fd

[Qemu-devel] [PATCH] Avoiding extra iterations while closing file fd

[Pankaj Gupta]

Avoiding iterations for fd 0, 1 & 2 when we are closing file fds in child process.

Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
---
 net/tap.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index 2d5099b..3253838 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -364,11 +364,8 @@ static int launch_script(const char *setup_script, const char *ifname, int fd)
     if (pid == 0) {
         int open_max = sysconf(_SC_OPEN_MAX), i;
 
-        for (i = 0; i < open_max; i++) {
-            if (i != STDIN_FILENO &&
-                i != STDOUT_FILENO &&
-                i != STDERR_FILENO &&
-                i != fd) {
+        for (i = 3; i < open_max; i++) {
+            if (i != fd) {
                 close(i);
             }
         }
@@ -449,11 +446,8 @@ static int net_bridge_run_helper(const char *helper, const char *bridge)
         char br_buf[6+IFNAMSIZ] = {0};
         char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) + 15];
 
-        for (i = 0; i < open_max; i++) {
-            if (i != STDIN_FILENO &&
-                i != STDOUT_FILENO &&
-                i != STDERR_FILENO &&
-                i != sv[1]) {
+        for (i = 3; i < open_max; i++) {
+            if (i != sv[1]) {
                 close(i);
             }
         }
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] Avoiding extra iterations while closing file fd

[Stefan Hajnoczi]

On Wed, Mar 12, 2014 at 10:24:27PM +0530, Pankaj Gupta wrote:
> Avoiding iterations for fd 0, 1 & 2 when we are closing file fds in child process.
> 
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
>  net/tap.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)

POSIX defines the values of standard in, out, and error as 0, 1, and 2
constants.  So this patch is correct but it doesn't do anything useful.
This is something compiler can optimize (but speed doesn't even matter
here).

Please try to focus on patches that fix bugs, add features, or otherwise
add value - it takes the community time to review, test, and merge
patches.

Thanks, applied to my net-next tree:
https://github.com/stefanha/qemu/commits/net-next

Stefan