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

From: "Richard W.M. Jones" <rjones(a)redhat.com&gt; To: "Thomas Schmitt" <scdbackup(a)gmx.net&gt; Cc: libguestfs(a)redhat.com, "Jiri Kucera" <jkucera(a)redhat.com&gt; 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_editio... > 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 build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW