On Wed, Mar 16, 2005 at 04:16:42PM -0500, Alan Altmark wrote: | On Wednesday, 03/16/2005 at 10:09 CST, Phil Howard | <[EMAIL PROTECTED]> wrote: | > But there is still missing documentation info. Is there a specific NAME | > that is accessed in the /tapes directory? Or is it like EL TORITO and | > it stores which name somewhere in the ISO header blocks? | > | > Or does someone have a small ISO image that can be booted that I can | > dissect and perhaps get the needed info? | | Sorry for not being clear. The ISO images have no idea of the tape file | names. They just issue READ CCW's to a tape drive.
The ISO filesystem would have the file names in its directory, but it would have no idea of the purpose being applied here. Booting a CD on a PC is done in a strange way, too. Sector 17 has a boot record that points (sector number?) to a boot catalog, which has entries for a number of purposes for boot images. These entries end up point to exact sectors of data, and apparently don't use file names at all. During ISO filesystem creation, or thereafter, a program such as "mkisofs" can find the specified images and construct these entries with appropriate pointers. I suspect part of the reason for the complexity was to avoid implementing the ISO-9660 filesystem in BIOS and having it search for names at boot time. It's not unlike how LILO works on a PC, where it builds a list of harddrive sectors. Things are stored in files, but the path to the data is all done by locating where the data blocks for the files are, and pointing that way. | The mapping to file name occurs completely within the tape emulator. It | has a "cursor" that moves byte-by-byte through the files listed in the | TDF. If you rewind the tape and IPL from it, the first 24 bytes from the | first file listed in the TDF area read in and control is transferred to | the loaded channel program. That program continues to read from the tape | starting at byte 25. Whether that's the same file or the next file in the | TDF is transparent to the channel program. | | The different files that make up a CD can be in any directory on the CD. | It is the TDF that specifies the files. When the IPL READ CCW is performed, exactly where on the CD does the tape emulator go to get the list of the files? Does it look for a specific name? Or does it do like El Torito and use a sector with some kind of catalog information that points to these files, either by name or by data sector? What program would be used to make an ISO image bootable? -- ----------------------------------------------------------------------------- | Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ | | (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ | ----------------------------------------------------------------------------- ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
