openssh unix dev - Aug 2006 - too many close calls for non-opened fds

Hello All,

I'm using OpenSSH 4.3p2 in HP-UX 11.23. On running tusc (a tool to trace 
system calls and signals) on sshd, I found lot of close calls upto 2047. 
Those close calls try to close a non-opened file descriptor and results in 
an error. This behaviour is seen only from OpenSSH 3.9 where closefrom() 
call is introduced to close the file descriptors before re-exec. The fix is 
to check the resource limits before calling close(), but the comment in 
source code (bsd-closefrom.c) says that it is not recommended to check the 
resource limits.  Is there anyway to fix this too many close() calls which 
results in performance degradation?

Relavant part of tusc output for sshd is given below,

...............
..............
set_userthreadid(1) ...................................... = 1
stat("/etc/pam_debug", 0x7ffff5b0) ....................... ERR#2
ENOENT
stat("/tcb/files/auth/system/default", 0x7fffec70) ....... ERR#2
ENOENT
getuid() ................................................. = 0 (0)
getuid() ................................................. = 0 (0)
getuid() ................................................. = 0 (0)
setgroups(0, NULL) ....................................... = 0
open("/dev/null", O_RDWR|0x800, 0123) .................... = 3
close(3) ................................................. = 0
sysconf(_SC_OPEN_MAX) .................................... = 2048
close(3) ................................................. ERR#9 EBADF
close(4) ................................................. ERR#9 EBADF
close(5) ................................................. ERR#9 EBADF
close(6) ................................................. ERR#9 EBADF
close(7) ................................................. ERR#9 EBADF
close(8) ................................................. ERR#9 EBADF
close(9) ................................................. ERR#9 EBADF
................
...............

On Mon, Aug 14, 2006 at 10:35:26AM +0530, Logu wrote:
> Is there anyway to fix this too many close() calls which 
> results in performance degradation?
is it really a performance degradation?

> On Mon, Aug 14, 2006 at 10:35:26AM +0530, Logu wrote:
>> Is there anyway to fix this too many close() calls which
>> results in performance degradation?
>
> is it really a performance degradation?
>
Yes, we see a performance degradation. We see approximately 30-40 new 
connections per second in our machine. In another machine we see the number 
of close calls go upto 60K.

I would like to know the impact of checking the resource limits before 
calling close().

thanks
-logu

On Wed, Aug 16, 2006 at 11:51:37PM +0530, Logu wrote:
> >On Mon, Aug 14, 2006 at 10:35:26AM +0530, Logu wrote:
> >>Is there anyway to fix this too many close() calls which
> >>results in performance degradation?
> >
> >is it really a performance degradation?
> >
> 
> Yes, we see a performance degradation. We see approximately 30-40 new 
> connections per second in our machine. In another machine we see the number
> of close calls go upto 60K.
> 
> I would like to know the impact of checking the resource limits before 
> calling close().
if a file is opened and the resource limit is decreased,
then looping to the resource limit will miss some open files.

--On Wednesday, August 16, 2006 10:56 PM +0200 Markus Friedl 
<markus.r.friedl at arcor.de> wrote:
> if a file is opened and the resource limit is decreased,
> then looping to the resource limit will miss some open files.
Does any UNIX variant have a "close all my open fds except for these" 
syscall? Or an easy way to get back a list of in-use fds? I really wish 
such a beast would be added, as calling close() on all possible fd numbers 
is _such_ a hack...

-- 
Carson