discussion related to implementation of File descriptor functions in RTEMS

[Sebastian Huber]

On 25/03/2020 20:33, Joel Sherrill wrote:

>
>
> On Wed, Mar 25, 2020 at 12:17 AM Eshan Dhawan <eshandhawan51 at gmail.com 
> <mailto:eshandhawan51 at gmail.com>> wrote:
>
>
>
>     On Wed, Mar 25, 2020 at 4:01 AM Joel Sherrill <joel at rtems.org
>     <mailto:joel at rtems.org>> wrote:
>
>
>
>         On Tue, Mar 24, 2020 at 4:57 PM Eshan Dhawan
>         <eshandhawan51 at gmail.com <mailto:eshandhawan51 at gmail.com>> wrote:
>
>             Hello everyone,
>             As @Vaibhav Gupta <mailto:vaibhav.varodek at gmail.com>
>             suggested I have also added adding file descriptor
>             functions to my GSOC project.
>             I went through the mailing list archives for more information.
>             RTEMS as its own file descriptor so the functions need to
>             be implemented from scratch.
>             I wanted to get more information related to it.
>
>
>         What's the set of functions you are proposing for those not
>         tracking your draft proposal?
>
>     Link:
>     https://docs.google.com/document/d/1n-JOFUbFn6V1kViAGWsEGbVHL9MxlMyKP0BbZhEA1Rs/edit?usp=sharing
>     I haven't searched about the functions in the list yet. The list
>     was made by Vaibhav, last year and he told me that it could be
>     added to proposal this year as well.
>     I read the archives that these need to be written from scratch.
>
>
>
> Maybe not. I found at least this implementation of renameat() which 
> was implemented on top of existing calls:
>
> https://github.com/lattera/freebsd/blob/master/contrib/openbsm/bin/auditdistd/renameat.h
>
> It should be in a C file but that shows it can be done. That directory 
> has a lot of these methods.

Adding the *at() functions with an RTEMS-specific implementation would 
be nice (and not difficult). The generic renameat() implementation for 
example changes the current directory. One of the goals of this API is 
to avoid exactly this. In glibc/Linux for example a system call is used:

https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/renameat.c;h=901d61f37e10d0c2df245c01bb2ef980d00e8f52;hb=HEAD

https://github.com/torvalds/linux/blob/master/fs/namei.c#L4590

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