From: Masatake YAMATO <yamato@redhat.com>
To: kzak@redhat.com
Cc: paithankarprasanna@gmail.com, util-linux@vger.kernel.org
Subject: Re: [RFC] ipcs for POSIX IPC
Date: Wed, 24 Apr 2024 22:15:17 +0900 (JST) [thread overview]
Message-ID: <20240424.221517.2073047999286647720.yamato@redhat.com> (raw)
In-Reply-To: <20240424095240.l2fzrswgtvaqpv2o@ws.net.home>
On Wed, 24 Apr 2024 11:52:40 +0200, Karel Zak wrote:
> On Wed, Apr 24, 2024 at 04:10:48AM +0530, Prasanna Paithankar wrote:
>> The 'ipcs' (and 'ipcrm') command provides information on (or removes
>> some) System V IPC resources. I'd like to know why no similar utility
>> for POSIX IPC has existed for a long time. I would like to know if
>> such a tool exists in case I missed it. If not, I will provide patches
>> to ipcs and ipcrm (or should I separate the functionality into a new
>> utility).
>
> I would suggest improving 'lsipc' instead of using the old 'ipcs'.
>
> The question is where to find information about POSIX IPC. For System
> V, there is /proc/sysvipc, but there is no equivalent for POSIX (or I
> am not aware of it). It seems that the only way to gather this
> information is by scanning all processes' memory maps for /dev/shm.
> This could be achieved by using lsfd.
I read the related man pages:
shm_overview(7) says shm_open(3) may make a file at /dev/shm.
With the following test prgram, I saw it created /dev/shm/X.
#include <sys/mman.h>
#include <sys/stat.h> /* For mode constants */
#include <fcntl.h> /* For O_* constants */
int
main(void)
{
int fd = shm_open("X", O_CREAT | O_EXCL | O_RDWR, 0600);
while (1);
return 0;
}
sem_overview(7) says:
On Linux, named semaphores are created in a virtual filesystem, nor‐
mally mounted under /dev/shm, with names of the form sem.somename.
As Karel wrote, lsfd can list them if a process do-mmap them.
lsfd doesn't distinguish shm and sem.
mq_overview(7) doesn't say the defatil about the visibility. I inspected the visibility
of mq when addng mq support to lsfd.
The list of mqueue is available if "mqueue" file systems is mounted.
See mqueue_fs_type in ipc/mqueue.c of Linux.
On Fedora, the filesystem is mounted to /dev/mqueue by default. However, some
platforms may not mount it by default.
Here is my idea for listing mqueue:
for mnt_ns in $all_mnt_ns; do
if mqueue_fs_is_found_in /proc/mounts; then
ls the_mount_point
else
for p in $all_processes; do
for fd in $all_fd_in_$p; do
if is_mqueue_fd $fd
echo the_information_about $fd
fi
done
done | uniq
fi
done
lsfd can list mqueues as far as they are opened by processes.
We can use get_minor_for_mqueue and is_mqueue_dev in lsfd-cmd/file.c
when implementing of is_mqueue_fd.
Mounting temporarily the mqueue file system in lsipc is an alternative
way.
Masatake YAMATO
> Karel
>
>>
>> Yours sincerely
>> Prasanna Paithankar
>>
>
> --
> Karel Zak <kzak@redhat.com>
> http://karelzak.blogspot.com
>
>
prev parent reply other threads:[~2024-04-24 13:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-23 22:40 [RFC] ipcs for POSIX IPC Prasanna Paithankar
2024-04-24 9:52 ` Karel Zak
2024-04-24 13:15 ` Masatake YAMATO [this message]
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