On Wed, 16 Jul 2003, Richard Troth wrote: > I found out, to my dismay, that the CMS FS driver > lacks needed functionality for 'mount -o loop' to work. > What I mean is that you cannot at this time have an EXT2 FS image > on a CMS minidisk and mount that with "-o loop". You can *copy* > the FS image file to another filesystem, so I know it's > not a matter of corrupted content. > > Learning ... learning ... > It turns out that "-o loop" requires a different function > in the VFS layer than those which CMS FS already supports. [sigh] > > So! What I have found thus far is that we need at least one of the > "address space" functions, and clearly "readpage" is getting > called. But the effect is a locked-up 'mount' command or worse: > > CMSFS: cmsfs_file_open(): opening file 'lxasetup.ext2fs' inode 507 > CMSFS: cmsfs_readpage(0x02E54380,0x00302DEC) > illegal operation: 0001 > CPU: 0 Tainted: P > Process loop0 (pid: 821, task: 0079a000, ksp: 0079be20) > Krnl PSW : 07082000 80000002 > Krnl GPRS: ffffffff 00000000 002a3514 00000000 > ... rest deleted for brevity ... > > Loopback mounts create a kernel process to handle the mapping > of the "file" to a pseudo block device, so the "loop0" above is > correct, and it does in fact have a PID like a user space process. > I just don't know what [loopx] does behind the scenes. > > Where can I find the operation of loopback mounts outlined? > It's not clear from kernel source nor from the Documentation directory.
It used to be that one had to use losetup to configure the loopback device first. Then the function got rolled into (from a user perpsective) to mount with '-o loop.' I've not explored, but I think the options are pretty-much just passed on to the kernel. Anyway, "man losetup" may help a little. > > -- R; > -- Cheers John. Join the "Linux Support by Small Businesses" list at http://mail.computerdatasafe.com.au/mailman/listinfo/lssb Copyright John Summerfield. Reproduction prohibited.
