Hello Chris,
Am 07.12.21 um 05:10 schrieb Chris Johns:
On 3/12/21 11:50 pm, Christian Mauderer wrote:
RTEMS untar implementation had problems with overwriting or integrating
archives into existing directory structures. This patch adapts the
behavior to mimic that of a GNU tar or BSD tar and extends the tar01
test to check for the behavior. That is:
* If a directory structure exists, the files from the archive will be
integrated. Existing files are overwritten.
What currently happens?
The untar fails if a directory exists that is in the archive. Note that
is mostly true if the archive contains directories and not only files.
That means: If I have two example archives that look like follows:
> tar tvf image-error.tar.gz
drwxr-xr-x christian_m/domainusers 0 2021-11-26 15:31 l1/
drwxr-xr-x christian_m/domainusers 0 2021-11-26 14:38 l1/l2/
-rw-r--r-- christian_m/domainusers 12 2021-11-26 14:27 l1/l2/x.txt
> tar tvf image-ok.tar.gz
-rw-r--r-- christian_m/domainusers 12 2021-11-26 14:27 l1/l2/x.txt
The first image contains the directories l1 and l1/l2 and the file
l1/l2/x.txt. The second contains only the l1/l2/x.txt.
With our current implementation, I would be able to extract the first
archive one times and a second try would fail because l1 and l1/l2
already exist. The second archive could be extracted multiple times and
would overwrite x.txt every time.
* If a file exists and the archive contains a directory with the same
name, the file is removed and a directory is created. In the above
example: if l1/l2 is a file it will be overwritten with a new
directory.
OK
* If a directory exists and the archive contains a file with the same
name, the directory will be replaced if it is empty. If it contains
files, the result is an error.
* An archive also can contain only a file without the parent
directories. If in that case one of the parent directories exists as a
file extracting the archive results in an error. In the example: if
l1/l2 is a file and the archive doesn't contain the directories but
only the file l1/l2/x.txt that would be an error.
* In case of an error, it is possible that the archive has been
partially extracted.
And what was there is not recoverable.
Correct. Note that I basically just tested what GNU and BSD tar do to
get a reference what is "expected behavior". See
https://devel.rtems.org/ticket/4552
There would be a number of other reasonable behaviors that could be
considered right too. But I think the default tar utilities are a good
reference.
Functionally this is not a big change and so I am left wondering why the
original developer(s) did not do this?
I think the original behavior of the code in RTEMS was a bit different.
I found a bug from 2019:
https://devel.rtems.org/ticket/3823
The solution to that bug solved the bug but changed the behavior of tar
a bit and introduced the new problem that tar can't integrate data into
existing directory structures.
I think the changes make sense and I do not think it will break any applications
I know of that use this code.
Thanks for reviewing it. I'll push the patch soon.
Best regards
Christian
Chris
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