[Xenomai-help] Shared memory and fstat()

[Xenomai-help] Shared memory and fstat()

[Herrera-Bendezu, Luis]

Hello,

Can a file descriptor returned from Xenomai POSIX skin
shm_open()/ftruncate() used in fstat()?

Value returned for st_size in the stat structure is
always 0 despite change of size using ftruncate().

Noticed that shared memory object does not have an entry
on /dev/shm as regular POSIX objects. Where is it located?
If entry exists, can it be used to query its size?

Thanks,
Luis

Re: [Xenomai-help] Shared memory and fstat()

[Gilles Chanteperdrix]

Herrera-Bendezu, Luis wrote:
> Hello,
> 
> Can a file descriptor returned from Xenomai POSIX skin
> shm_open()/ftruncate() used in fstat()?

No.

> 
> Value returned for st_size in the stat structure is
> always 0 despite change of size using ftruncate().
> 
> Noticed that shared memory object does not have an entry
> on /dev/shm as regular POSIX objects. Where is it located?
> If entry exists, can it be used to query its size?

No, xenomai posix skin shared memory do not exist as filesystem objects,
they will only be listed in /proc/xenomai/heap.

Note, however, that they are only useful for sharing memory between
kernel-space posix applications and user-space posix applications, which
should have become rare these days. If what you are looking for is
simply a way for sharing memory between to user-space real-time
applications, they you can use linux regular shared memories, for which
fstat works.

> 
> Thanks,
> Luis
> 
> _______________________________________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help
> 


-- 
					    Gilles.

Re: [Xenomai-help] Shared memory and fstat()

[Herrera-Bendezu, Luis]

Gilles,

>-----Original Message-----
>From: Gilles Chanteperdrix [mailto:gilles.chanteperdrix@xenomai.org
>Sent: Wednesday, June 16, 2010 4:40 PM
>To: Herrera-Bendezu, Luis
>Cc: xenomai@xenomai.org
>Subject: Re: [Xenomai-help] Shared memory and fstat()
>
>
>Herrera-Bendezu, Luis wrote:
>> Hello,
>> 
>> Can a file descriptor returned from Xenomai POSIX skin
>> shm_open()/ftruncate() used in fstat()?
>
>No.
>
>> 
>> Value returned for st_size in the stat structure is
>> always 0 despite change of size using ftruncate().
>> 
>> Noticed that shared memory object does not have an entry
>> on /dev/shm as regular POSIX objects. Where is it located?
>> If entry exists, can it be used to query its size?
>
>No, xenomai posix skin shared memory do not exist as 
>filesystem objects,
>they will only be listed in /proc/xenomai/heap.
>
>Note, however, that they are only useful for sharing memory between
>kernel-space posix applications and user-space posix 
>applications, which
>should have become rare these days. If what you are looking for is
>simply a way for sharing memory between to user-space real-time
>applications, they you can use linux regular shared memories, for which
>fstat works.
>
That is precisely what I am looking for.

Thanks,
Luis
>> 
>> Thanks,
>> Luis
>> 
>> _______________________________________________
>> Xenomai-help mailing list
>> Xenomai-help@domain.hid
>> https://mail.gna.org/listinfo/xenomai-help
>> 
>
>
>-- 
>					    Gilles.
>