Glenn, I think the only portable way is to do a open(".", O_RDONLY),
and if that fails save the name from getcwd(), and restore that, if
neither /dev/fd or /proc/${pid}/fd/${dirfd} are working. As far as I
know there is no way to open a file using <dev,ino>, and <dev,ino> may
not be reliable for all kinds of file systems, such like as fuse
(http://en.wikipedia.org/wiki/Filesystem_in_Userspace).
Olga
On Thu, Aug 16, 2012 at 1:24 AM, ольга крыжановская
<olga.kryzhanov...@gmail.com> wrote:
> Glenn, how to an application obtain a fd just using <dev,ino>?
>
> The alternative, if no /proc or /dev/fd is available, is to save the
> cwd, do a temporary cwd using fchdir(), and restore the old cwd. This
> is now glibc did it, with a mutex around the whole sequence to make it
> thread safe.
>
> Olga
>
> On Thu, Aug 16, 2012 at 1:20 AM, Glenn Fowler <g...@research.att.com> wrote:
>>
>> On Thu, 16 Aug 2012 01:09:29 +0200 =?KOI8-R?B?z8zYx8Egy9LZ1sHOz9fTy8HR?=
>> wrote:
>>> Glenn, have you ever considered putting an openat(), fstatat(),
>>> mkfifoat() emulation into libast, if the base operating system does
>>> not have such calls? I have been trying more tests with the at() apis
>>> but I am not happy to trash much of libshell with lots of #ifdef
>>> AT_CWD tests if there is a better option.
>>
>>> AFAIK a lot of the at() calls can be emulated by using
>>> /dev/fd/${dirfd}/${path} or /proc/${pid}/fd/${dirfd}/${path}. I just
>>> do not know, are there cases where /dev/fd or /proc/${pid}/fd are not
>>> available (chroot environments?)?
>>
>> there are a lot of systems with lame or no /proc
>> and it will be hard to work around systems with no O_search
>>
>> but let me think a bit on that
>> if we didn't have to worry about dir fd's across exec (probably rare right
>> now)
>> we might be able to cache emulated open(O_search) paths with <dev,ino> keys
>> on systems that don't support /dev/fd/<FD>/<PATH> pr
>> /proc/<PID>/fd/<FD>/<PATH>
>>> Olga
>>> --
>>> , _ _ ,
>>> { \/`o;====- Olga Kryzhanovska -====;o`\/ }
>>> .----'-/`-/ olga.kryzhanov...@gmail.com \-`\-'----.
>>> `'-..-| / http://twitter.com/fleyta \ |-..-'`
>>> /\/\ Solaris/BSD//C/C++ programmer /\/\
>>> `--` `--`
>>
>
>
>
> --
> , _ _ ,
> { \/`o;====- Olga Kryzhanovska -====;o`\/ }
> .----'-/`-/ olga.kryzhanov...@gmail.com \-`\-'----.
> `'-..-| / http://twitter.com/fleyta \ |-..-'`
> /\/\ Solaris/BSD//C/C++ programmer /\/\
> `--` `--`
--
, _ _ ,
{ \/`o;====- Olga Kryzhanovska -====;o`\/ }
.----'-/`-/ olga.kryzhanov...@gmail.com \-`\-'----.
`'-..-| / http://twitter.com/fleyta \ |-..-'`
/\/\ Solaris/BSD//C/C++ programmer /\/\
`--` `--`
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