[DragonFlyBSD - Submit #2776] (Closed) [PATCH RFC] sbin/hammer: add hammer volume-erase command

Tue Jan 27 11:34:12 PST 2015

Issue #2776 has been updated by tkusumi.

Status changed from In Progress to Closed

Closing the ticket. After having some talk on irc with tuxillo and a few other people on libhammer's goal, I've realized code integration of libhammer (which did exist for years but not completed) is the first thing to be done.

If that's ever finished implementing a new hammer command as well as outbox application will be much easier. This command should be implemented in less than +100 lines of code.

However I'll be working on it on my local repository for now before I ever start to send them. There isn't anything technically difficult on libhammer code integration since all the hammer utilities do use ioctls everywhere, however it needs to be carefully done so as not to break anything that's already working as production. If the integration ever gets matured and stabilized I may send them.

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Submit #2776: [PATCH RFC] sbin/hammer: add hammer volume-erase command
http://bugs.dragonflybsd.org/issues/2776#change-12567

* Author: tkusumi
* Status: Closed
* Priority: Normal
* Assignee: tuxillo
* Category: Userland
* Target version: 4.2.x
----------------------------------------
This RFC patch adds a new hammer command "volume-erase". It erases the hammer volume signature (0xC8414D4DC5523031) or the entire header without using dd. It aims to do the following.

Currently hammer doesn't allow you to volume-add a volume with the signature, even if the volume is not currently used (mounted). When adding a volume, ioctl reads the volume header sector and see if the signature exists. If it does exist then the ioctl tells you to erase it using dd on dmesg. This is right behavior as it protects users from possible operation error, however forcing users to manually do dd is too low level IMO. Filesystem should provide a way to do that with its userspace utility and it's not difficult to implement it with some safety measures.

There isn't anything new in terms of implementation because hammer's userspace already has all the functionalities to do this. It simply finds existing hammer filesystems using getmntinfo(3) and then check each volume to make sure it's currently not used. If it's ok to erase it overwrites the signature or the entire header with 0 after 5 seconds of grace periods. Specifying "header" keyword makes this command erase whole volume header instead of just signature.

Note that hammer volume-del command also erases the signature when removing a device from filesystem and it does that in kernel space. volume-erase command erases the signature by simply memset(3)ing 0 to ondisk structure of the volume header and then write(2) it because it's possible to do it that way with less code change (no need to add another ioctl like HAMMERIOC_ERASE_VOLUME only to expose hammer_clear_volume_header() functionality to userspace).

Also note that this patch moves some code from sbin/hammer/cmd_pseudofs.c to sbin/hammer/misc.c as independent functions that are available from hammer userspace, instead of being static functions, as they are general enough for other hammer commands to use. volume-erase command uses them to do user interaction before erasing.

-----
some examples

// newfs some devices independently and mount /dev/ad1
# newfs_hammer -L TEST /dev/ad1 > /dev/null
# newfs_hammer -L TEST /dev/ad2 > /dev/null
# newfs_hammer -L TEST /dev/ad3 > /dev/null
# mount_hammer /dev/ad1 /HAMMER

// erase signature
# hammer volume-add /dev/ad2 /HAMMER
hammer volume-add ioctl: Inappropriate file type or format
# dmesg
...
hammer_volume_add: Formatting of valid HAMMER volume TEST denied. Erase with dd or hammer volume-erase!
An error occurred: 79
# od -N 16 -tx1 -Ax /dev/ad2
0000000    31  30  52  c5  4d  4d  41  c8  00  00  04  00  00  00  00  00
0000010
# hammer volume-erase /dev/ad2
You have requested that volume signature of /dev/ad2 be erased
Do you really want to do this? y
Erasing volume signature of /dev/ad2 5 4 3 2 1
Erased
# od -N 16 -tx1 -Ax /dev/ad2
0000000    00  00  00  00  00  00  00  00  00  00  04  00  00  00  00  00
0000010
# hammer volume-add /dev/ad2 /HAMMER
# hammer volume-list /HAMMER
/dev/ad1
/dev/ad2

// erase the entire header
# hammer volume-add /dev/ad3 /HAMMER
hammer volume-add ioctl: Inappropriate file type or format
# dmesg
...
hammer_volume_add: Formatting of valid HAMMER volume TEST denied. Erase with dd or hammer volume-erase!
An error occurred: 79
hammer_volume_add: Formatting of valid HAMMER volume TEST denied. Erase with dd or hammer volume-erase!
An error occurred: 79
# od -N 1928 -tx1 -Ax /dev/ad3
0000000    31  30  52  c5  4d  4d  41  c8  00  00  04  00  00  00  00  00
0000010    00  00  04  04  00  00  00  00  00  00  04  14  00  00  00  00
0000020    00  00  00  00  19  00  00  00  00  00  00  00  00  00  00  00
0000030    56  1d  07  07  21  a3  e4  11  8f  a0  09  00  27  00  47  c3
0000040    ac  63  dc  61  38  6e  dc  11  85  13  01  30  1b  b8  a9  f5
0000050    54  45  53  54  00  00  00  00  00  00  00  00  00  00  00  00
0000060    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00
*
...
# hammer volume-erase /dev/ad3 header
You have requested that volume header of /dev/ad3 be erased
Do you really want to do this? y
Erasing volume header of /dev/ad3 5 4 3 2 1
Erased
# od -N 1928 -tx1 -Ax /dev/ad3
0000000    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00
*
0000780
# hammer volume-add /dev/ad3 /HAMMER
# hammer volume-list /HAMMER
/dev/ad1
/dev/ad2
/dev/ad3

// try to erase an already erased volume
# umount /HAMMER
# hammer volume-erase /dev/ad3 header
You have requested that volume header of /dev/ad3 be erased
Do you really want to do this? y
Erasing volume header of /dev/ad3 5 4 3 2 1
Erased
# hammer volume-erase /dev/ad3 signature
hammer volume-erase: /dev/ad3 is already erased
# hammer volume-erase /dev/ad3 header
hammer volume-erase: /dev/ad3 is already erased

// try to erase a volume used by mounted HAMMER filesystem
# mount | grep ROOT
ROOT on / (hammer, local)
# hammer volume-list /
/dev/serno/VB1679fd54-1faff0a7.s1d
# hammer volume-erase /dev/serno/VB1679fd54-1faff0a7.s1d
hammer volume-erase: /dev/serno/VB1679fd54-1faff0a7.s1d is used by /
# echo $?
1

---Files--------------------------------
0001-sbin-hammer-add-hammer-volume-erase-command.patch (14.7 KB)

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