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Date: Wed, 21 Oct 2015 15:33:56 +0300
From: Andrey Repin <anrdaemon AT yandex DOT ru>
Reply-To: cygwin AT cygwin DOT com
Message-ID: <1598393077.20151021153356@yandex.ru>
To: Corinna Vinschen <cygwin AT cygwin DOT com>, cygwin AT cygwin DOT com
Subject: Re: Error accessing mapped drive >2TB?
In-Reply-To: <20151021100328.GL5319@calimero.vinschen.de>
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Greetings, Corinna Vinschen!

>> > The only thing I can think of is that the 2nd drive is >2TB.
>> 
>> The same thing happens here with a 3.1 TB Fusion drive and a 500 GB external drive, so no, I don’t think the volume size is the real issue.
>> 
>> I assume you are seeing the same thing that I am, that Explorer shows the root contents of both drives just fine?
>> 
>> When I strace’d an ls of one of these root shares here, I got 764 lines of…emissions, of which this section seems the most interesting to me:
>> 
>> 1051  263166 [main] ls 4720 stat64: entering
>>   625  263791 [main] ls 4720 normalize_posix_path: src /p
>>   609  264400 [main] ls 4720 normalize_posix_path: /p = normalize_posix_path (/p)
>>   630  265030 [main] ls 4720 mount_info::conv_to_win32_path: conv_to_win32_path (/p)
>>   653  265683 [main] ls 4720 mount_info::cygdrive_win32_path: src '/p', dst 'P:\'
>>   668  266351 [main] ls 4720 set_flags: flags: binary (0x2)
>>   674  267025 [main] ls 4720 mount_info::conv_to_win32_path: src_path /p, dst P:\, flags 0x4022, rc 0
>>  1168  268193 [main] ls 4720 symlink_info::check: 0x0 = NtCreateFile (\??\P:\)
>> 10641  278834 [main] ls 4720 symlink_info::check_reparse_point: NtFsControlFile(FSCTL_GET_REPARSE_POINT) failed, 0xC0000275
>>   839  279673 [main] ls 4720 symlink_info::check: not a symlink
>>  1049  280722 [main] ls 4720 symlink_info::check: 0 = symlink.check(P:\, 0x24B620) (0x4022)
>>   655  281377 [main] ls 4720 path_conv::check: this->path(P:\), has_acls(0)
>>   640  282017 [main] ls 4720 stat_worker: got 5 error from path_conv
>>   757  282774 [main] ls 4720 __set_errno: int stat_worker(path_conv&, stat*):1933 setting errno 5
>>   714  283488 [main] ls 4720 stat_worker: -1 = (\??\P:\,0x600042080)
>> 
>> Why errno 5 from path_conv?

> Probably because of the above

>   symlink_info::check_reparse_point: NtFsControlFile(FSCTL_GET_REPARSE_POINT)
>   failed, 0xC0000275

> This is in fact a weird error code in this scenario.

> Consider that symlink_info::check_reparse_point is *only* called, if the
> file to check (here "P:\") has the FILE_ATTRIBUTE_REPARSE_POINT flag
> set.  So from the Windows perspective it is certainly a reparse point.

> Cygwin checks the flag to allow evaluating of reparse points as symlinks.
> If the flag is set, it calls symlink_info::check_reparse_point which in
> turn calls

>   status = NtFsControlFile (..., FSCTL_GET_REPARSE_POINT, ...);

> to fetch the target information the reparse point points to, in POSIX
> terms the symlink target.  But *this* call returns a status of 0xC0000275,
> which means STATUS_NOT_A_REPARSE_POINT.  And since it's totally unexpected
> that NtFsControlFile fails on a reparse point, the code sets errno to EIO.

> Hang on.

> The FILE_ATTRIBUTE_REPARSE_POINT flag is set but when calling a function
> to fetch the reparse data it's no reparse point anymore?  How dumb is
> that?

That's… interesting.
Windows does not allow for reparse points to networked locations.
Symlinks all right, directory junctions no.

> I can't reproduce this bug with my Samba drives, but it's not actually a
> bug in Cygwin from my perspective.

> Yeah, that observation doesn't really help, so I applied a potential
> workaround to Cygwin.  If you're set up to build your own Cygwin, please
> give it a try.  Otherwise I'll upload a new snapshot in the next couple of
> days.


-- 
With best regards,
Andrey Repin
Wednesday, October 21, 2015 15:32:13

Sorry for my terrible english...