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Re: handling of reparse points

From: Stefan Kueng <tortoisesvn_at_gmail.com>
Date: Thu, 7 Jun 2018 18:50:59 +0200

On 05.06.2018 23:35, Philip Martin wrote:
> Stefan Küng <tortoisesvn_at_gmail.com> writes:
>
>> Index: subversion/libsvn_subr/io.c
>> ===================================================================
>> --- subversion/libsvn_subr/io.c (revision 1831874)
>> +++ subversion/libsvn_subr/io.c (working copy)
>> @@ -342,8 +342,11 @@
>> /* Not using svn_io_stat() here because we want to check the
>> apr_err return explicitly. */
>> SVN_ERR(cstring_from_utf8(&path_apr, path, pool));
>> -
>> +#ifdef WIN32
>> + flags = APR_FINFO_MIN;
>> +#else
>> flags = resolve_symlinks ? APR_FINFO_MIN : (APR_FINFO_MIN | APR_FINFO_LINK);
>> +#endif
>> apr_err = apr_stat(&finfo, path_apr, flags, pool);
>>
>> if (APR_STATUS_IS_ENOENT(apr_err))
>>
>
> This needs a comment to explain why Windows needs to do something
> different.

patch with comment attached.

> I think we would have to back this change out if we ever attempted to
> add svn:special support on Windows, but I suppose any such support is
> unlikely in the near future; as Branko pointed out CreateSymbolicLink
> doesn't have the semantics we want.

Just FYI: in that case svn would have a requirement for NTFS. Because
both hard links (for files) and junctions (for directories) only work on
NTFS. So it wouldn't be possible anymore to use svn on e.g. a usb stick
formatted with FAT32.

> Making .svn a symbolic link on Linux came up in another thread recently:
>
> https://lists.apache.org/thread.html/d08f3a0b71600e2b67cd39817cd99e4de25a7e4f12817fe451f162e5@%3Cdev.subversion.apache.org%3E
>
> At present there is an assumption that .svn lives on the same filesystem
> as the working copy and that files can be atomically moved from .svn/tmp
> into the working copy (see workqueue.c calling svn_io_file_rename2). If
> .svn becomes a symlink that points to a different filesystem then these
> moves fail and Subversion doesn't work. We might be able to work around
> this by replacing svn_io_file_rename2 with svn_io_file_move.
>
> I don't know if Windows has the same problem.

On Windows, the MoveFileEx() API which is used by win32_file_rename
which is used by svn_io_file_rename2 can work that way: the flag
MOVEFILE_COPY_ALLOWED must be passed as well. Then the Move works across
volumes because Windows then does the move as a copy/delete instead.

Also: the current implementation on Windows handles links wrong: it
assumes that a reparse point is always a junction, but that's not the
case. A junction is just a special form of a reparse point.

Stefan

Received on 2018-06-07 18:51:15 CEST

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