Re: [XEN RFC for-4.14] Re: use of "stat -"

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.06.2020 15:31, Ian Jackson wrote:
> Jan Beulich writes ("Re: [XEN RFC for-4.14] Re: use of "stat -""):
>> Looking at vfs_statx() in the kernel, I can't see any provisions to
>> get at the data without traversing the specified path.
> 
> The question is what "traversing the path" means.
> 
> How do you explain this ?
> 
> $ >t
> $ exec 3>t
> $ stat -L -c '%F %i' /dev/stdin <&3
> regular empty file 421124
> $ ll /dev/stdin <&3
> lrwxrwxrwx 1 root root 15 Jun  7 02:01 /dev/stdin -> /proc/self/fd/0
> $ ll /proc/self/fd/0 <&3
> l-wx------ 1 ian ian 64 Jun 25 14:29 /proc/self/fd/0 -> /home/ian/t
> $ mv t u
> $ ll /proc/self/fd/0 <&3
> l-wx------ 1 ian ian 64 Jun 25 14:29 /proc/self/fd/0 -> /home/ian/u
> $ rm u
> $ ll /proc/self/fd/0 <&3
> l-wx------ 1 ian ian 64 Jun 25 14:29 /proc/self/fd/0 -> '/home/ian/u 
> (deleted)'
> $ stat -L -c '%F %i' /dev/stdin <&3
> regular empty file 421124
> $ ll -Li /dev/stdin <&3
> 421124 -rw-rw-r-- 0 ian ian 0 Jun 25 14:28 /dev/stdin
> $
> 
> Clearly it isn't actually following this synthetic symlink to
> "/home/ian/u (deleted)".

Okay, so there's clearly some trickery then which don't know where
to find.

Jan