svn commit: r321839 - in head: share/man/man4 share/man/man5 sys/fs/fdescfs sys/kern sys/sys

[Chagin Dmitry]

On Tue, Aug 01, 2017 at 03:40:19AM +0000, Dmitry Chagin wrote:
> Author: dchagin
> Date: Tue Aug  1 03:40:19 2017
> New Revision: 321839
> URL: https://svnweb.freebsd.org/changeset/base/321839
> 
> Log:
>   Implement proper Linux /dev/fd and /proc/self/fd behavior by adding
>   Linux specific things to the native fdescfs file system.
>   
>   Unlike FreeBSD, the Linux fdescfs is a directory containing a symbolic
>   links to the actual files, which the process has open.
>   A readlink(2) call on this file returns a full path in case of regular file
>   or a string in a special format (type:[inode], anon_inode:<file-type>, etc..).
>   As well as in a FreeBSD, opening the file in the Linux fdescfs directory is
>   equivalent to duplicating the corresponding file descriptor.
>   
>   Here we have mutually exclusive requirements:
>   - in case of readlink(2) call fdescfs lookup() method should return VLNK
>   vnode otherwise our kern_readlink() fail with EINVAL error;
>   - in the other calls fdescfs lookup() method should return non VLNK vnode.
>   
>   For what new vnode v_flag VV_READLINK was added, which is set if fdescfs has beed
>   mounted with linrdlnk option an modified kern_readlinkat() to properly handle it.
>   
>   For now For Linux ABI compatibility mount fdescfs volume with linrdlnk option:
>   
>       mount -t fdescfs -o linrdlnk null /compat/linux/dev/fd
>   
>   Reviewed by:	kib@
>   MFC after:	1 week
>   Relnotes:	yes

Differential Revision:		https://reviews.freebsd.org/D11452