[Bug-tar] GNU tar fails to treat leading slash consistently

[Stan Sieler]

Hi,

GNU tar 1.14

(This is my first email to any GNU bug report destination, so please forgive me
if I screwed up protocol-wise.)

I had a bug report from one of my users, which boils down to:

He did:
             tar cvf foo.tar /fum
followed by:
             tar xvf foo.tar /fum
which failed with: 
             tar: /fum: Not found in archive

This seems to reflect two bugs in GNU tar (one fairly important, since it
cost us a day of work, and relatively minor).

We create a backup of our NFS server by doing:
 
      tar --totals --index-file=backup.index -cRf backup.tar /c
 
   GNU tar responds:
 
      tar: Removing leading `/' from member names
 
   and proceeds to copy the files to the file "backup.tar", generating a list of
   files stored in the file "backup.index". 

   (We know we could use -P, of course.)

Bug 1:
 
   GNU tar fails to strip the leading slash when looking for a file to restore 
(and -P 
   is not specified).  (Example failure shown earlier.)
 
   Argument in favor of interpreting this behavior as a bug:

      If it removes it at "c" time, it should remove it at "x" time!

   (I.e., consistency)

   Note that fixing this will not hurt existing tar users ... I doubt any do
   things like:

            tar cvf ... /something  (i.e., no "-P")

   and then *count* on: tar xvf ... /something  *FAILING*.

   Thus, if tar suddenly starts treating "/something" as "something" for an "x",
   it will not cause backward incompatibilities.

Bug 2 (minor, misnamed keyword)

   (Background: the index file shows each file with a leading slash, even 
without -P)
 
   The "index-file" option is misnamed ... it does not create a file containing
   the list of files *on* the tape, but a list of files copied *to* the tape.

   The distinction is important :)
 
   The man page correctly documents "--index-file" as:

      send verbose output to FILE instead of stdout
   
   ...note the lack of the word "index".  

   Elsewhere, we see that "verbose output" includes a list of files 
   *processed* (i.e., the index file correctly has a list of the 
   original names, including leading slash).  

   I see three fixes:

      1. rename the option to list-of-processed-files 
         (and quietly recognize "index-file" as a synonym for it)
 
      2. have the index-file should contain the de-slashed names, and truly be 
an index file.
 
      3. fix bug 1 above, which allows filenames from the current index file 
(with leading
         slashes) to be provided (unedited) as input to "x" (i.e., having the 
file be
         a usable index file again).  (With this fix, one might consider noting 
in the
         documentation that "index-file"is a historical mistake for the option 
name,
         or change the documentation to state that it *is* a list of files on 
the tape,
         in case we find future cases where the files-on-tape differ from 
files-processed.)

thanks!
 
-- 
Stan Sieler
work:     www.allegro.com
personal: www.sieler.com/wanted/index.html