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Re: /dev/fd/N not synonymous with file descriptor N; it is on Linux




On Dec 16 13:36, Wayne Davison wrote:
> On Sun, Dec 16, 2018 at 12:29 PM Corinna Vinschen wrote:
> > In contrast to Linux the symlinks are not just faked symlinks with the underlying OS having direct access to the file descriptors.
> 
> Yeah, Linux is more like a fuse where the open filehandles are used
> directly on open, and the stat calls return pretend symlinks with the
> lsof info.
> 
> > The way it's implemented in Cygwin uses the actual file path resolution and then either works or fails as above.
> 
> If Cygwin can't be changed into a fuse idiom, perhaps a hard-link
> idiom could be used? For instance, when the /proc/$PID/fd/0 symlink is
> being created, the code could try to hard-link the file to
> /proc/$PID/.fd/0 first

Nice try, but hardlinks don't cross FS borders.  /proc is a filesystem
on its own with its own inode numbers.

I'm mulling over adding some hack to open().  It could try to recognize
the special case of opening a processes' own descriptor symlink within
/proc and then warp the open() call into dup().  No idea how tricky
or even feasible that is, though...


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer

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