[Libguestfs] Consider to replace isoinfo by own code rather than by xorriso

[Richard W.M. Jones]

On Wed, May 26, 2021 at 07:17:52PM -0400, Jiri Kucera wrote:
> Hi Rich,
>
> if you are still interested, you can try iso-info utility from
> libcdio package (distributed with RHEL 9).

In the end we went with parsing the PVD directly:
https://github.com/libguestfs/libguestfs/blob/master/daemon/isoinfo.ml

Rich.

> Jiri
> 
> ----- Original Message -----
> > From: "Richard W.M. Jones" <rjones at redhat.com>
> > To: "Thomas Schmitt" <scdbackup at gmx.net>
> > Cc: libguestfs at redhat.com, "Jiri Kucera" <jkucera at redhat.com>
> > Sent: Tuesday, March 30, 2021 11:22:49 PM
> > Subject: Re: [Libguestfs] Consider to replace isoinfo by own code rather than by xorriso
> > 
> > On Tue, Mar 30, 2021 at 10:57:07PM +0200, Thomas Schmitt wrote:
> > > Hi,
> > > 
> > > thank you for flying xorriso. :))
> > > 
> > > But as its author and looking at
> > > 
> > >   https://github.com/libguestfs/libguestfs/blob/master/daemon/isoinfo.ml
> > > 
> > > i feel obliged to point out that using it as replacement for isoinfo
> > > will increase the consumption of RAM and CPU cycles substantially.
> > > 
> > > xorriso command -indev loads the whole directory tree of the ISO filesystem
> > > with names and metadata. Depending on that tree this can be dozens of
> > > megabytes and lots of insertion operations in a not much optimized tree
> > > model.
> > 
> > "megabytes" may not be a problem - and in fact hasn't been in my
> > testing.  Could it grow unbounded?
> > 
> > > On the other hand it is quite uncomplicated to implement an own ISO 9660
> > > PVD reader and to become independent of any external program for that
> > > purpose.
> > > 
> > > The Primary Volume Descriptor begins at LBA 16 (= byte offset 32768).
> > > Its layout is described in ECMA-119 8.4 (note: BP = byte offset + 1)
> > >   https://www.ecma-international.org/wp-content/uploads/ECMA-119_4th_edition_june_2019.pdf
> > > or in HTML at
> > >   https://wiki.osdev.org/ISO_9660#The_Primary_Volume_Descriptor
> > > 
> > > E.g. the info missing in xorriso's output of -pvd_info is at offsets:
> > > 
> > >    80 -  87 iso_volume_space_size
> > >             (unsigned 32 bit, little endian first, then again as big
> > >             endian)
> > > 
> > >   124 - 127 iso_volume_sequence_number
> > >             (unsigned 16 bit, little endian first, then again as big
> > >             endian)
> > > 
> > >   128 - 131 iso_logical_block_size
> > >             (unsigned 16 bit, little endian first, then again as big
> > >             endian)
> > >             (If you don't read 2048 here, then you are in unchartered
> > >              territory.)
> > > 
> > > The date format for e.g. iso_volume_creation_t at offset 813 - 829
> > > is a decimal digit string YYYMMDDhhmmsshh with a trailing binary byte
> > > value for the time zone with 15 minutes granularity. ("hh" means
> > > hundredths of seconds.)
> > > See also
> > >   https://wiki.osdev.org/ISO_9660#Numerical_formats
> > >   https://wiki.osdev.org/ISO_9660#Date.2Ftime_format
> > 
> > OK, thanks.
> > 
> > Rich.
> > 
> > --
> > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> > Read my programming and virtualization blog: http://rwmj.wordpress.com
> > Fedora Windows cross-compiler. Compile Windows programs, test, and
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> > 

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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