Re: tarfs: fails to read tar.gz files.

[Cyril Roelandt]

On 08/22/2012 03:34 AM, Cyril Roelandt wrote:
> Hi !
>
> I've just tried tarfs, and it seems to me that it does not handle tar.gz
> files very well. I got the code from the Hurd incubator, compiled it,
> and ran the following commands to create a simple tar.gz file:
>
> $ mkdir -p a/b/c
> $ touch a/foo
> $ touch a/b/c/bar
> $ tar czvf foobar.tar.gz a/
>
> Here is what I got when trying to run tarfs:
>
> $ settrans -ca ./foobar ./tarfs -z ./foobar.tar.gz -D -
> gzip_open: Underlying file size is 183 bytes
> gzip_read_header: Gzip compression method: 0x08
> gzip_open: start_file_offs = 10
> gzip_stream_read: End of file
> gzip_stream_read: offset file/zip = 10 / 0
> gzip_stream_read: avail in/out = 173 / 8192
> gzip_stream_read: requested/read = 8192 / 8192
> gzip_stream_read: offset file/zip = 170 / 8192
> gzip_stream_read: avail in/out = 13 / 8192
> gzip_stream_read: End of stream
> gzip_verify_crc: Valid gzip CRC
> gzip_verify_crc: Valid gzip uncompressed stream size (10240)
> gzip_stream_read: requested/read = 8192 / 2048
> traverse: file traversed (offset file/zip = 175 / 10240)
> gzip_open: Uncompressed stream size is 10240
> gzip_stream_read: End of file
> gzip_stream_read: offset file/zip = 10 / 0
> gzip_stream_read: avail in/out = 173 / 512
> gzip_error: zlib error: stream error
> gzip_stream_read: requested/read = 512 / 0
> ./tarfs: Read error (offset=0): Invalid argument
> settrans: ./tarfs: Translator died
>
>
> I think this is caused by the call to ZIP_DECOMPRESS in the "ZIP
> (stream_read)" function. It fails when stream->next_out is NULL (cf.
> http://www.zlib.net/manual.html : inflate() returns Z_STREAM_ERROR if
> the next_out field is NULL).
>
> stream->next_out is set in zipstores.c, at line 370:
>
> stream->next_out = (uchar *) buf;
>
> "buf" is a parameter of the "ZIP (stream_read)" function, which is
> called by the "ZIP (read)" function:
>
> static error_t
> ZIP (read) (struct store *store,
> store_offset_t offset, size_t index, size_t amount, void **buf,
> size_t *len)
> {
> ...
> }
>
> This function is called with *buf == NULL, which, I think, leads to the
> failure of tarfs.

OK, Ludovic Courtès and I looked at this issue today, and I think the 
following patch fixes the issue:

diff --git a/tar.c b/tar.c
index e7391f9..65f94b3 100644
--- a/tar.c
+++ b/tar.c
@@ -119,7 +119,7 @@ static union record *
 tar_get_next_record (struct archive *archive)
 {
     error_t err;
-    void *buf = NULL;
+    void *buf = mmap(NULL, RECORDSIZE, PROT_READ|PROT_WRITE, 
MAP_ANONYMOUS, 0, 0);
     size_t n = 0;

     err = store_read (archive->tar_file, 
archive->current_tar_position, RECORDSIZE, &buf, &n);



WBR,
Cyril Roelandt.