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Diffstat (limited to 'open_issues/xen_crash_copy-size_le_page_size.mdwn')
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diff --git a/open_issues/xen_crash_copy-size_le_page_size.mdwn b/open_issues/xen_crash_copy-size_le_page_size.mdwn new file mode 100644 index 00000000..f2d8081e --- /dev/null +++ b/open_issues/xen_crash_copy-size_le_page_size.mdwn @@ -0,0 +1,104 @@ +[[!meta copyright="Copyright © 2009 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_xen]] + +`/dev/hd2` is 2 GiB in size (backed by LVM), unformatted. + + # mkfs.ext2 -o hurd /dev/hd2 + mke2fs 1.41.7 (29-June-2009) + hd2 count 1 + re-open, hd2 count 2 + ext2fs_check_if_mount: Can't check if filesystem is mounted due to missing mtab file while determining whether /dev/hd2 is mounted. + re-open, hd2 count 3 + re-open, hd2 count 4 + re-open, hd2 count 5 + Filesystem label= + OS type: Hurd + Block size=4096 (log=2) + Fragment size=4096 (log=2) + 131072 inodes, 524288 blocks + 26214 blocks (5.00%) reserved for the super user + First data block=0 + Maximum filesystem blocks=536870912 + 16 block groups + 32768 blocks per group, 32768 fragments per group + 8192 inodes per group + Superblock backups stored on blocks: + 32768, 98304, 163840, 229376, 294912 + + Assertion `copy->size <= PAGE_SIZE' failed in file "../gnumach-1-branch-Xen-branch/xen/block.c", line 536 + Kernel Breakpoint trap, eip 0x20020a77 + Stopped at 0x20020a76: int $3 + db> trace + 0x20020a76(2006abc1,2006ba03,2006782c,218,2e2be8d4) + 0x20020ace(2006ba03,2006782c,218,2e3629a0,32000) + 0x2003e9d5(2de04764,2e2be0b8,12,0,3fff80) + 0x200476e6(2de5ad54,2e2db010,2e30a9a0,2de3a854,2de5ad44) + 0x20021ed4(2de5ad44,2e2bb2e0,2e2bb2a0,0,0) + 0x2005309d(129b8f0,3,38,28,e) + 0x20006838(129b8f0,3,38,28,e) + >>>>> user space <<<<< + + + $ addr2line -i -f -e /boot/gnumach-xen 0x20020a76 0x20020ace 0x2003e9d5 0x200476e6 0x20021ed4 0x2005309d 0x20006838 + Debugger + /home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/debug.c:105 + Assert + ??:0 + device_write + /home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/xen/block.c:537 + _Xdevice_write + /home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/device/device.server.c:253 + ipc_kobject_server + /home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/ipc_kobject.c:201 + mach_msg_trap + /home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/ipc/mach_msg.c:1367 + mach_call_call + /home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/i386/i386/locore.S:1083 + +GDB on `mkfs.ext2`: + + raw_write_blk (channel=0x80829d8, data=0x8082a40, block=524272, count=8, buf=0x80a0a60) at ../../../git/lib/ext2fs/unix_io.c:272 + 272 actual = write(data->dev, buf, size); + (gdb) print size + $4 = 32768 + (gdb) bt + #0 raw_write_blk (channel=0x80829d8, data=0x8082a40, block=524272, count=8, buf=0x80a0a60) at ../../../git/lib/ext2fs/unix_io.c:272 + #1 0x080635fc in unix_write_blk64 (channel=0x80829d8, block=524272, count=8, buf=0x80a0a60) at ../../../git/lib/ext2fs/unix_io.c:673 + #2 0x0806373c in unix_write_blk (channel=0x80829d8, block=524272, count=8, buf=0x80a0a60) at ../../../git/lib/ext2fs/unix_io.c:705 + #3 0x0805e87d in ext2fs_zero_blocks (fs=0x8082940, blk=524272, num=16, ret_blk=0x15ffb1c, ret_count=0x0) + at ../../../git/lib/ext2fs/mkjournal.c:182 + #4 0x0804ec56 in main (argc=131072, argv=0x80000) at ../../git/misc/mke2fs.c:2032 + +Discussion: + + <tschwinge> I had a look at the code, but unfortunately don't really know + how this data transfers between Xen and the domU work. + <tschwinge> Well, I know how it roughly works, but not the implementation + deatils. + <youpi> well here it's not about the xen/domU transfers + <youpi> it's about copying data to align it + <youpi> i.e. when offset is not aligned, I need to copy it + <tschwinge> Yes- + <youpi> I was lazy, just implemented it for things smaller than a page + <youpi> it just needs to be extended into copying several pages + <tschwinge> youpi: Hmm, do we need to copy all the data to shift away the + offset or is there a better way? + <youpi> the blkbackend needs data to be sector-aligned + <youpi> just aligning on a page makes offset computation simpler + <youpi> as it's rare that's not a problem + <tschwinge> And a sector is the usual 512 bytes there, I assume? + <tschwinge> But then we do need to copy all of it? + <youpi> let me check + <youpi> the sector is the granularity you can't go below + <youpi> sector is the sector_size reported by the backend + <youpi> but for sector_number and first/last_sect it's 512 + <youpi> yes, that's weird |