[Tarantool-patches] [PATCH v6] vinyl: fix check vinyl_dir existence at bootstrap

[Alexander Turenko]

Please, resend the patchset to Nikita Pettik and Aleksandr Lyapunov (because it
is related to vinyl).

Or extract this particular path to its own branch and send it as a singleton
patch.

WBR, Alexander Turenko.

On Thu, Aug 20, 2020 at 05:25:38PM +0300, Alexander V. Tikhonov wrote:
> Hi Alexander, thanks a lot for your help. As we discussed the commit
> message I've made all the changes in it and commited to branch.

I think it is good enough. LGTM.

Cited below for the history.

> commit e18b7e8f56787a9099429ff9e6fc6c1185d74723
> Author: Alexander V. Tikhonov <avtikhon at tarantool.org>
> Date:   Fri Aug 14 11:18:25 2020 +0300
> 
>     vinyl: fix check vinyl_dir existence at bootstrap
>     
>     During implementation of openSUSE build with testing got failed test
>     box-tap/cfg.test.lua. Found that when memtx_dir didn't exist and
>     vinyl_dir existed and also errno was set to ENOENT, box configuration
>     succeeded, but it shouldn't. Reason of this wrong behavior was that
>     not all of the failure paths in xdir_scan() set errno, but the caller
>     assumed it.
>     
>     Debugging the issue found that after xdir_scan() there was incorrect
>     check for errno when it returned negative values. xdir_scan() is not
>     system call and negative return value from it doesn't mean that errno
>     would be set too. Found that in situations when errno was left from
>     previous commands before xdir_scan() and xdir_scan() returned negative
>     value by itself it produced the wrong check.
>     
>     The previous failed logic of the check was to catch the error ENOENT
>     which set in the xdir_scan() function to handle the situation when
>     vinyl_dir was not exist. It failed, because checking ENOENT outside
>     the xdir_scan() function, we had to be sure that ENOENT had come from
>     xdir_scan() function call indeed and not from any other functions
>     before. To be sure in it possible fix could be reset errno before
>     xdir_scan() call, because errno could be passed from any other function
>     before call to xdir_scan().
>     
>     As mentioned above xdir_scan() function is not system call and can be
>     changed in any possible way and it can return any result value without
>     need to setup errno. So check outside of this function on errno could
>     be broken.
>     
>     To avoid of it we must avoid of errno checks outside of the function.
>     Better solution is to use the flag in xdir_scan(), to check if the
>     directory should exist. So errno check was removed and instead of it
>     the check for vinyl_dir existence using flag added.
>     
>     Closes #4594
>     Needed for #4562
>     
>     Co-authored-by: Alexander Turenko <alexander.turenko at tarantool.org>