Re: bash from local mounted drive with subst command

[Thomas Wolff <towo@towo.net>]

Am 21.02.2022 um 00:56 schrieb Takashi Yano:
> On Mon, 21 Feb 2022 08:41:52 +0900
> Takashi Yano wrote:
>> On Sun, 20 Feb 2022 22:38:53 +0100
>> Claude TETE wrote:
>>> A bash in a local mounted drive, use realpath instead of mounted one
>>> for all child processes.
>>>
>>> Example, mount a local folder on Z: drive, go in there and run any
>>> external command:
>>> $ subst Z: C:\\Users
>>> $ cd /cygdrive/z/
>>> $ /bin/pwd
>>> /cygdrive/c/Users
>>>
>>> Expected
>>> /cygdrive/w
>> This is since:
>>
>> commit 19d59ce75d5301ae167b421111d77615eb307aa7
>> Author: Corinna Vinschen <corinna@vinschen.de>
>> Date:   Fri May 7 16:07:03 2021 +0200
>>
>>      Cygwin: path_conv: Rework handling native symlinks as inner path components
>>
>>      commit 456c3a46386f was only going half-way.  It handled symlinks and
>>      junction points as inner path components and made realpath return the
>>      correct path, but it ignored drive letter substitution, i. e., virtual
>>      drives created with, e. g.
>>
>>        subst X: C:\foo\bar
>>
>>      It was also too simple.  Just returning an error code from
>>      symlink_info::check puts an unnecessary onus on the symlink evaluation
>>      loop in path_conv::check.
>>
>>      Rework the code to use GetFinalPathNameByHandle, and only do this after
>>      checking the current file for being a symlink failed.
>>
>>      If the final path returned by GetFinalPathNameByHandle is not the same
>>      as the incoming path, replace the incoming path with the POSIXified
>>      final path.  This also short-circuits path evaluation, because
>>      path_conv::check doesn't have to recurse over the inner path components
>>      multiple times if all symlinks are of a native type, while still getting
>>      the final path as end result.
>>
>>      Virtual drives are now handled like symlinks.  This is a necessary change
>>      from before to make sure virtual drives are handled identically across
>>      different access methods.  An example is realpath(1) from coreutils.  It
>>      doesn't call readlink(2), but iterates over all path components using
>>      lstat/readlink calls.  Both methods should result in the same real path.
>>
>>      Fixes: 456c3a46386f ("path_conv: Try to handle native symlinks more sanely")
>>      Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
>>
>>
>> The behaviour is by design. Does this cause any practical issue?
> The similar happens also in Linux.
>
> In Debuan GNU/Linux 11.2:
> yano@debian:~$ mkdir -p a/b/c
> yano@debian:~$ ln -s a/b/c c
> yano@debian:~$ cd c
> yano@debian:~/c$ pwd
> /home/yano/c
> yano@debian:~/c$ /bin/pwd
> /home/yano/a/b/c
>
> In cygwin 3.3.4:
> yano@cygwin:~$ mkdir -p a/b/c
> yano@cygwin:~$ ln -s a/b/c c
> yano@cygwin:~$ cd c
> yano@cygwin:~/c$ pwd
> /home/yano/c
> yano@cygwin:~/c$ /bin/pwd
> /home/yano/a/b/c
pwd -P will also work like /bin/pwd - but: subst is more comparable to 
mount than to ln -s