fdescfs

[fullauto2012]

I've working on getting authpf working and the man page says it requires fdescfs to be mounted to run... I'm a completely unaware of what fdescfs even does? Been looking around, but everything I found with a reference to fdescfs just assumes you know what it does and why it's required...

Can anyone shed some light on this?

 

[wblock@]

Well, there's fdescfs(5)...

 

[fullauto2012]

"The file-descriptor file system, or fdescfs, provides access to the per-
process file descriptor namespace in the global file system namespace.
The conventional mount point is /dev/fd.

The file system's contents appear as a list of numbered files which cor-
respond to the open files of the process reading the directory. The
files /dev/fd/0 through /dev/fd/# refer to file descriptors which can be
accessed through the file system. If the file descriptor is open and the
mode the file is being opened with is a subset of the mode of the exist-
ing descriptor, the call:"

Ok... I guess what I'm asking is what is the file descriptor namespace that is mentioned?
I read this, and that seems to be where I got hung up...

 

[Murph]

File descriptors are just an integer index into a per-process array in the kernel of all of the process' open files and file-like devices. Members of that array are data structures used by the kernel to direct the I/O between devices / files and user code. It starts with stdin == 0, stdout == 1, stderr ==2, then the next file opened by the process will be 3, and so on.

 

[kpa]

This is something I've wondering, how is fdescfs(5) any different from the devfs(8) created /dev/fd directory? As far as I can see the file descriptors provided by devfs(8) do exactly what you'd expect them to do.

 

[Murph]

This is something I've wondering, how is fdescfs(5) any different from the devfs(8) created /dev/fd directory? As far as I can see the file descriptors provided by devfs(8) do exactly what you'd expect them to do.

I believe that devfs(5) only has stdin, stdout, and stderr by default, created in
sys/kern/kern_descrip.c:fildesc_drvinit().

fdescfs(5) dynamically populates the directory at runtime, in sys/fs/fdescfs/fdesc_vnops.c, where the implementation of lookup() and readdir() reference the current set of FDs on each call.