[Pkg-libburnia-devel] Bug#1010098: xorriso: please allow -cut-out directly from block devices

[Thomas Schmitt]

Hi,

Ivan Shmakov wrote:
> An alternative would be to check if it’s possible to seek to
> specified positions rather than to the end of file

This should work now, by an attempt of  lseek(wanted_size, SEEK_SET) if
lseek(0, SEEK_END) yields failure or 0 size.
(libisoburn commit 0c0d542, libisofs commit c6cb7df)

Nevertheless, the attempt to read from /dev/zero still yields failure,
because lseek() returns 0 when it is supposed to return the new offset
position.
This is already so in your example with strace and dd:
> lseek(0, 2560, SEEK_CUR)                = 0

Actually i think that the behavior of lseek() with /dev/zero is not
conformant with man 2 lseek:

  RETURN VALUE
    Upon successful completion, lseek() returns the resulting offset loca‐
    tion as measured  in bytes from the beginning of the file.  On error,
    the value (off_t) -1 is returned.

The xorriso code does not ask for offset 0. So the lseek() call does not
succeed if the resulting offset is 0. So the return value should be -1.


If non-random-access file content is desired and can be produced with
repeatable size, then consider to define a filter by -external_filter
and attach it to a file by -set_filter. The file may be inserted with an
arbitrary file as source. The filter program is free to ignore it and to
do its own thing.

-------------------------------------------------------------------

> if the target file is created in a yet-nonexistent
> directory, the directory created inherits the permissions
> of the source file as well (only adding +x where there’s r.)

This is an intentional feature introduced in 2008. SVN rev 1643, now git
commit a44e7db9:
  Bug fix: Implicite directory attribute copying with -cut_out was wrong
There are reasons why this makes sense if the disk file's permissions
are restrictive and its parent's permissions are liberal.

Embarrassingly, only a week later i introduced automatic file splitting,
controlled by command -split_size, where this peculiar source of directory
permissions would make even more sense.
But function Xorriso_graft_split() inserts a new directory with the
permissions of the parent directory in the ISO.

I have now corrected this to the behavior of -cut_out and documented it
with both commands in the man page:

  -cut_out disk_path byte_offset byte_count iso_rr_path
         ...
         E.g.
         ...
          -cut_out /my/disk/file 4094m 2047m \
            /file/part_3_of_3_at_4094m_with_2047m_of_5753194821
         If the directory /file does no yet exist, then  its  permissions
         are   not   taken   from  directory  /my/disk  but  rather  from
         /my/disk/file with additional x-permission for  those  who  have
         r-permission.
  ...
  -split_size number["k"|"m"]
         ...
         The  newly  created  ISO directory inherits its permissions from
         the data file with additional x-permission for  those  who  have
         r-permission.

(libisoburn commit 5aac3dd)

-------------------------------------------------------------------

Then there was the problem of -paste_in not working with devices which
are suitable for -cut_out (and thus not being the reverse operation of
-cut_out).
I changed -paste_bin so that it is willing to work with the same files
as target which -cut_out would accept as source (modulo permissions, of
course).
(libisoburn commit 865115f)


Have a nice day :)

Thomas