Hi,
the old patch didn't work very well (deadlocks with writeable snapshots).
I made a better one. It includes tow ioctls required for xfs.
On Mon, 19 Nov 2001, Anselm Kruis wrote:
> Hi,
>
> I have made a new writeable snapshot patch against latest cvs. It consists
> of a kernel patch and a patch for lvchange. The patch is based on previous
> work from Dale J. Stephenson <steph@connex.com>.
>
> If you create a snapshot, the snapshot is still read-only at first. You
> can now use lvchange, to make the snapshot writeable. Use it i.e. to
> repair file systems on the snapshot.
>
> lvcreate -s -n snap ...
> lvchange -p rw /dev/vg00/snap
> e2fsck # or something similar
> sync
> lvchange -p r /dev/vg00/snap
> mount -o ro /dev/vg00/snap ....
>
> The kernel patch consists mainly of two parts:
> - the actual COW remapping for the snapshot
> - an ioctl to let the user space tools detect the presence of the
> writeable snapshot support in the kernel.
>
> The later ist required, because current kernels have no protection against
> making a snapshot-LV writeable. The protection is in lvchange. If you
> make a snapshot-LV writeable, the writes end on the original volume.
> Bad bad bad. :-(
> Therefore lvchange needs a way to detect the presence of writeable
> snapshot support in the kernel.
>
> I decided to add a new ioctl on the /dev/lvm device: LVM_GET_FEATURE_BITS.
> The ioctl returns a bit field. Every set bit indicates the presence of a
> feature. If the ioctl is not present, no features are present. For now the
> only feature defined is: LVM_FEATURE_WRITEABLE_SNAPSHOTS.
>
> Known Problems:
> ---------------
>
> - If a writeable snapshot runs out of space, all processes writing to the
> snapshot hang.
fixed
>
> - Needs more testing.
>
> Comments and criticism are very much appreciated.
>
> Anselm Kruis
> Software Engineer
>
>
The diff is against the current cvs version of LVM as of Jan 01 2002
diff -c -r -b -B -N -x CVS LVM.vanilla/PATCHES/linux-2.4.15-writeable-snapshots.patch LVM/PATCHES/linux-2.4.15-writeable-snapshots.patch
*** LVM.vanilla/PATCHES/linux-2.4.15-writeable-snapshots.patch Thu Jan 1 01:00:00 1970
--- LVM/PATCHES/linux-2.4.15-writeable-snapshots.patch Sun Nov 18 11:05:14 2001
***************
*** 0 ****
--- 1,27 ----
+ diff -u --recursive --new-file linux-2.4.15pre4.vanilla/Documentation/Configure.help linux/Documentation/Configure.help
+ --- linux-2.4.15pre4.vanilla/Documentation/Configure.help Sun Nov 18 10:46:17 2001
+ +++ linux/Documentation/Configure.help Sat Nov 17 22:55:13 2001
+ @@ -1693,6 +1693,13 @@
+ want), say M here and read <file:Documentation/modules.txt>. The
+ module will be called lvm-mod.o.
+
+ +Support for writeable snapshots
+ +CONFIG_LVM_WRITEABLE_SNAPSHOTS
+ + The LVM driver allows you to make snapshots of a logocal volume.
+ + Usually these snapshots are read-only. This options add support for
+ + writeable snapshots. You can use a writeable snapshot to run a
+ + filesystem check on the snapshot prior to mounting it.
+ +
+ Multiple devices driver support (RAID and LVM)
+ CONFIG_MD
+ Support multiple physical spindles through a single logical device.
+ diff -u --recursive --new-file linux-2.4.15pre4.vanilla/drivers/md/Config.in linux/drivers/md/Config.in
+ --- linux-2.4.15pre4.vanilla/drivers/md/Config.in Fri Sep 14 23:22:18 2001
+ +++ linux/drivers/md/Config.in Sat Nov 17 22:41:02 2001
+ @@ -14,5 +14,6 @@
+ dep_tristate ' Multipath I/O support' CONFIG_MD_MULTIPATH $CONFIG_BLK_DEV_MD
+
+ dep_tristate ' Logical volume manager (LVM) support' CONFIG_BLK_DEV_LVM $CONFIG_MD
+ +dep_mbool ' Support for writeable snapshots' CONFIG_LVM_WRITEABLE_SNAPSHOTS $CONFIG_BLK_DEV_LVM $CONFIG_EXPERIMENTAL
+
+ endmenu
diff -c -r -b -B -N -x CVS LVM.vanilla/kernel/lvm.c LVM/kernel/lvm.c
*** LVM.vanilla/kernel/lvm.c Tue Jan 1 21:49:48 2002
--- LVM/kernel/lvm.c Tue Jan 1 22:04:01 2002
***************
*** 214,219 ****
--- 214,220 ----
* in the LV each time. [AED]
* 12/10/2001 - Use add/del_gendisk() routines in 2.4.10+
* 01/11/2001 - Backport read_ahead change from Linus kernel [AED]
+ * 01/01/2002 - Support for writeable snapshots [A.Kruis@science-computing.de]
*
*/
***************
*** 374,379 ****
--- 375,385 ----
ushort lvm_iop_version = LVM_DRIVER_IOP_VERSION;
int loadtime = 0;
const char *const lvm_name = LVM_NAME;
+ ushort lvm_feature_bits =
+ #ifdef CONFIG_LVM_WRITEABLE_SNAPSHOTS
+ LVM_FEATURE_WRITEABLE_SNAPSHOTS |
+ #endif
+ 0;
/* volume group descriptor area pointers */
***************
*** 717,722 ****
--- 723,735 ----
/* Main command switch */
switch (command) {
+ case LVM_GET_FEATURE_BITS:
+ /* return a the feature bits. These bits indicate particular
+ features supported by this kernel. */
+ if (copy_to_user(arg, &lvm_feature_bits, sizeof(ushort)) != 0)
+ return -EFAULT;
+ return 0;
+
case LVM_LOCK_LVM:
/* lock the LVM */
return lvm_do_lock_lvm();
***************
*** 1063,1068 ****
--- 1076,1084 ----
return -EFAULT;
break;
+ case BLKBSZGET:
+ case BLKBSZSET:
+ return blk_ioctl (inode->i_rdev, command, a);
case HDIO_GETGEO:
/* get disk geometry */
***************
*** 1293,1298 ****
--- 1309,1315 ----
lv_t *lv = vg_this->lv[LV_BLK(minor)];
+ restart:
down_read(&lv->lv_lock);
if (!(lv->lv_status & LV_ACTIVE)) {
printk(KERN_ALERT
***************
*** 1381,1389 ****
goto out;
if (lv->lv_access & LV_SNAPSHOT) { /* remap snapshot */
! if (lvm_snapshot_remap_block(&rdev_map, &rsector_map,
! pe_start, lv) < 0)
goto bad;
} else if (rw == WRITE || rw == WRITEA) { /* snapshot origin */
lv_t *snap;
--- 1398,1425 ----
goto out;
if (lv->lv_access & LV_SNAPSHOT) { /* remap snapshot */
! int ret;
! ret = lvm_snapshot_remap_block(&rdev_map, &rsector_map,
! pe_start, lv);
! if (ret < 0)
goto bad;
+ if (ret > 0 || !(rw == WRITE || rw == WRITEA))
+ goto out; /* already remapped or read access */
+
+ #ifdef CONFIG_LVM_WRITEABLE_SNAPSHOTS
+ /* remap the block */
+
+ /* Serializes the COW with the accesses to the
+ snapshot device.
+
+ __remap_snapshot acquires the write lock. */
+ up_read(&lv->lv_lock);
+ __remap_snapshot(rdev_map, rsector_map,
+ pe_start, lv, vg_this);
+ goto restart;
+ #else
+ goto bad;
+ #endif
} else if (rw == WRITE || rw == WRITEA) { /* snapshot origin */
lv_t *snap;
diff -c -r -b -B -N -x CVS LVM.vanilla/kernel/lvm.h LVM/kernel/lvm.h
*** LVM.vanilla/kernel/lvm.h Tue Jan 1 21:49:48 2002
--- LVM/kernel/lvm.h Thu Nov 29 22:06:46 2001
***************
*** 72,77 ****
--- 72,78 ----
* 22/06/2001 - added Andreas Dilger's PE on 4k boundary alignment enhancements
* 19/07/2001 - added rwsem compatibility macros for 2.2 kernels
* 13/11/2001 - reduced userspace inclusion of kernel headers to a minimum
+ * 18/11/2001 - added defines for LVM_GET_FEATURE_BITS ioctl [A.Kruis]
*
*/
***************
*** 368,374 ****
--- 369,384 ----
/* This is actually the same as _IO ( 0xff, 0x00), oops. Remove for IOP 12+ */
#define LVM_LOCK_LVM _IO ( 0xfe, 0x100)
#endif
+ /* get lvm feature bits */
+ #define LVM_GET_FEATURE_BITS _IOR ( 0xfe, 0x9b, 1)
/* END ioctls */
+
+
+ /*
+ * Feature Bits
+ */
+ /* makeing a snapshot witeable is save */
+ #define LVM_FEATURE_WRITEABLE_SNAPSHOTS 0x01
/*
diff -c -r -b -B -N -x CVS LVM.vanilla/tools/lib/liblvm.h LVM/tools/lib/liblvm.h
*** LVM.vanilla/tools/lib/liblvm.h Tue Jan 1 21:49:48 2002
--- LVM/tools/lib/liblvm.h Thu Nov 29 22:06:46 2001
***************
*** 409,414 ****
--- 409,415 ----
void lvm_dont_interrupt ( int);
int lvm_get_col_numbers ( char *, long **);
int lvm_get_iop_version ( void);
+ int lvm_get_feature_bits ( void);
void lvm_init(int argc, char **argv);
void lvm_interrupt ( void);
int lvm_lock ( void);
diff -c -r -b -B -N -x CVS LVM.vanilla/tools/lib/lvm_get_feature_bits.c LVM/tools/lib/lvm_get_feature_bits.c
*** LVM.vanilla/tools/lib/lvm_get_feature_bits.c Thu Jan 1 01:00:00 1970
--- LVM/tools/lib/lvm_get_feature_bits.c Mon Nov 19 19:49:11 2001
***************
*** 0 ****
--- 1,60 ----
+ /*
+ * tools/lib/lvm_get_iop_version.c
+ *
+ * Copyright (C) 2001 Anselm Kruis
+ *
+ * November 2001
+ *
+ *
+ * This LVM library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This LVM library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this LVM library; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA
+ *
+ */
+
+ /*
+ * Changelog
+ *
+ * 18/11/2001 - created
+ *
+ */
+
+ #include <liblvm.h>
+
+ int lvm_get_feature_bits ( void) {
+ int group = -1;
+ int ret = 0;
+ ushort lvm_feature_bits = 0;
+
+ debug_enter ( "lvm_get_feature_bits -- CALLED\n");
+
+ /* just to ensure existance of /dev/lvm interface special */
+ lvm_check_special ();
+
+ if ( ( group = open ( LVM_DEV, O_RDONLY)) == -1)
+ ret = -LVM_ELVM_IOP_VERSION_OPEN;
+ else if ( ( ret = ioctl ( group, LVM_GET_FEATURE_BITS,
+ &lvm_feature_bits)) == -1) ret = -errno;
+ debug ( "lvm_get_feature_bits -- AFTER ioctl ret: %d\n", ret);
+ if ( group != -1) close ( group);
+ /* older kernels didn't have this IOCTL */
+ if ( -ret == EINVAL ) {
+ ret = 0;
+ lvm_feature_bits = 0; /* no special features */
+ }
+ if ( ret == 0) ret = lvm_feature_bits;
+
+ debug_leave ( "lvm_get_feature_bits -- LEAVING with ret: %d\n", ret);
+ return ret;
+ }
diff -c -r -b -B -N -x CVS LVM.vanilla/tools/lvchange.c LVM/tools/lvchange.c
*** LVM.vanilla/tools/lvchange.c Wed Jul 25 16:52:19 2001
--- LVM/tools/lvchange.c Mon Nov 19 19:46:12 2001
***************
*** 323,334 ****
continue;
}
! if ( lv->lv_access & LV_SNAPSHOT) {
fprintf ( stderr, "%s -- change on snapshot logical "
"volume \"%s\" not allowed\n", cmd, lv_name);
continue;
}
if ( lv->lv_access & LV_SNAPSHOT_ORG) {
fprintf ( stderr, "%s -- change on logical volume \"%s\" under "
"snapshot not allowed\n", cmd, lv_name);
--- 323,345 ----
continue;
}
! if ( ( lv->lv_access & LV_SNAPSHOT) &&
! ( (opt_C) || (opt_a) || (opt_r))) {
fprintf ( stderr, "%s -- change on snapshot logical "
"volume \"%s\" not allowed\n", cmd, lv_name);
continue;
}
+ if ( ( lv->lv_access & LV_SNAPSHOT) && (opt_p)) {
+ int feature_bits = lvm_get_feature_bits();
+ if ( feature_bits < 0 || !(feature_bits & LVM_FEATURE_WRITEABLE_SNAPSHOTS)) {
+ fprintf ( stderr, "%s -- change on snapshot logical "
+ "volume \"%s\" not allowed\n", cmd, lv_name);
+ continue;
+ }
+ }
+
+ /* fixme: opt_p should be save */
if ( lv->lv_access & LV_SNAPSHOT_ORG) {
fprintf ( stderr, "%s -- change on logical volume \"%s\" under "
"snapshot not allowed\n", cmd, lv_name);
***************
*** 364,370 ****
if ( doit > 0) {
doit_sum++;
! lv->lv_access = lv_access;
if ( opt_v > 0) printf ( "%s -- changing access permissions "
"of logical volume \"%s\"\n",
cmd, lv_name);
--- 375,383 ----
if ( doit > 0) {
doit_sum++;
! /* don't clear access flags except for LV_WRITE and LV_READ */
! lv->lv_access &= ~( LV_READ | LV_WRITE ) | lv_access;
! lv->lv_access |= lv_access;
if ( opt_v > 0) printf ( "%s -- changing access permissions "
"of logical volume \"%s\"\n",
cmd, lv_name);
---
Anselm Kruis Tel. +49 (0)89-356386-74
science + computing ag FAX +49 (0)89-356386-37
Ingolstädter Str. 22 mailto: A.Kruis@science-computing.de
D-80807 München WWW: http://www.science-computing.de/
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