From 1d330ec6f9186bda04fdf63ed513cd0cc84bd102 Mon Sep 17 00:00:00 2001 From: Milan Broz Date: Wed, 28 Mar 2012 18:41:23 +0100 Subject: dm: document sysfs entries Describe attributes provided by device-mapper in /sys/block. Signed-off-by: Milan Broz Signed-off-by: Alasdair G Kergon --- Documentation/ABI/testing/sysfs-block-dm | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-block-dm (limited to 'Documentation') diff --git a/Documentation/ABI/testing/sysfs-block-dm b/Documentation/ABI/testing/sysfs-block-dm new file mode 100644 index 0000000..87ca569 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-block-dm @@ -0,0 +1,25 @@ +What: /sys/block/dm-/dm/name +Date: January 2009 +KernelVersion: 2.6.29 +Contact: dm-devel@redhat.com +Description: Device-mapper device name. + Read-only string containing mapped device name. +Users: util-linux, device-mapper udev rules + +What: /sys/block/dm-/dm/uuid +Date: January 2009 +KernelVersion: 2.6.29 +Contact: dm-devel@redhat.com +Description: Device-mapper device UUID. + Read-only string containing DM-UUID or empty string + if DM-UUID is not set. +Users: util-linux, device-mapper udev rules + +What: /sys/block/dm-/dm/suspended +Date: June 2009 +KernelVersion: 2.6.31 +Contact: dm-devel@redhat.com +Description: Device-mapper device suspend state. + Contains the value 1 while the device is suspended. + Otherwise it contains 0. Read-only attribute. +Users: util-linux, device-mapper udev rules -- cgit v1.1 From fe878f34df89ad4af758f40bbec829807dc93a00 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Wed, 28 Mar 2012 18:41:24 +0100 Subject: dm thin: correct comments Remove documentation for unimplemented 'trim' message. I'd planned a 'trim' target message for shrinking thin devices, but this is better handled via the discard ioctl. Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/thin-provisioning.txt | 10 ---------- 1 file changed, 10 deletions(-) (limited to 'Documentation') diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt index 1ff044d..da50347 100644 --- a/Documentation/device-mapper/thin-provisioning.txt +++ b/Documentation/device-mapper/thin-provisioning.txt @@ -237,16 +237,6 @@ iii) Messages Deletes a thin device. Irreversible. - trim - - Delete mappings from the end of a thin device. Irreversible. - You might want to use this if you're reducing the size of - your thinly-provisioned device. In many cases, due to the - sharing of blocks between devices, it is not possible to - determine in advance how much space 'trim' will release. (In - future a userspace tool might be able to perform this - calculation.) - set_transaction_id Userland volume managers, such as LVM, need a way to -- cgit v1.1 From c4a69ecdb463a901b4645230613961e134e897cd Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Wed, 28 Mar 2012 18:41:28 +0100 Subject: dm thin: relax hard limit on the maximum size of a metadata device The thin metadata format can only make use of a device that is <= THIN_METADATA_MAX_SECTORS (currently 15.9375 GB). Therefore, there is no practical benefit to using a larger device. However, it may be that other factors impose a certain granularity for the space that is allocated to a device (E.g. lvm2 can impose a coarse granularity through the use of large, >= 1 GB, physical extents). Rather than reject a larger metadata device, during thin-pool device construction, switch to allowing it but issue a warning if a device larger than THIN_METADATA_MAX_SECTORS_WARNING (16 GB) is provided. Any space over 15.9375 GB will not be used. Signed-off-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/thin-provisioning.txt | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt index da50347..a119fbd 100644 --- a/Documentation/device-mapper/thin-provisioning.txt +++ b/Documentation/device-mapper/thin-provisioning.txt @@ -75,10 +75,12 @@ less sharing than average you'll need a larger-than-average metadata device. As a guide, we suggest you calculate the number of bytes to use in the metadata device as 48 * $data_dev_size / $data_block_size but round it up -to 2MB if the answer is smaller. The largest size supported is 16GB. +to 2MB if the answer is smaller. If you're creating large numbers of +snapshots which are recording large amounts of change, you may find you +need to increase this. -If you're creating large numbers of snapshots which are recording large -amounts of change, you may need find you need to increase this. +The largest size supported is 16GB: If the device is larger, +a warning will be issued and the excess space will not be used. Reloading a pool table ---------------------- -- cgit v1.1 From 2dd9c257fbc243aa76ee6db0bb8371f9f74fad2d Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Wed, 28 Mar 2012 18:41:28 +0100 Subject: dm thin: support read only external snapshot origins Support the use of an external _read only_ device as an origin for a thin device. Any read to an unprovisioned area of the thin device will be passed through to the origin. Writes trigger allocation of new blocks as usual. One possible use case for this would be VM hosts that want to run guests on thinly-provisioned volumes but have the base image on another device (possibly shared between many VMs). Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/thin-provisioning.txt | 39 ++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt index a119fbd..310c120 100644 --- a/Documentation/device-mapper/thin-provisioning.txt +++ b/Documentation/device-mapper/thin-provisioning.txt @@ -169,6 +169,38 @@ ii) Using an internal snapshot. dmsetup create snap --table "0 2097152 thin /dev/mapper/pool 1" +External snapshots +------------------ + +You can use an external _read only_ device as an origin for a +thinly-provisioned volume. Any read to an unprovisioned area of the +thin device will be passed through to the origin. Writes trigger +the allocation of new blocks as usual. + +One use case for this is VM hosts that want to run guests on +thinly-provisioned volumes but have the base image on another device +(possibly shared between many VMs). + +You must not write to the origin device if you use this technique! +Of course, you may write to the thin device and take internal snapshots +of the thin volume. + +i) Creating a snapshot of an external device + + This is the same as creating a thin device. + You don't mention the origin at this stage. + + dmsetup message /dev/mapper/pool 0 "create_thin 0" + +ii) Using a snapshot of an external device. + + Append an extra parameter to the thin target specifying the origin: + + dmsetup create snap --table "0 2097152 thin /dev/mapper/pool 0 /dev/image" + + N.B. All descendants (internal snapshots) of this snapshot require the + same extra origin parameter. + Deactivation ------------ @@ -254,7 +286,7 @@ iii) Messages i) Constructor - thin + thin [] pool dev: the thin-pool device, e.g. /dev/mapper/my_pool or 253:0 @@ -263,6 +295,11 @@ i) Constructor the internal device identifier of the device to be activated. + external origin dev: + an optional block device outside the pool to be treated as a + read-only snapshot origin: reads to unprovisioned areas of the + thin target will be mapped to this device. + The pool doesn't store any size against the thin devices. If you load a thin target that is smaller than you've been using previously, then you'll have no access to blocks mapped beyond the end. If you -- cgit v1.1 From 67e2e2b281812b5caf4923a38aadc6b89e34f064 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Wed, 28 Mar 2012 18:41:29 +0100 Subject: dm thin: add pool target flags to control discard Add dm thin target arguments to control discard support. ignore_discard: Disables discard support no_discard_passdown: Don't pass discards down to the underlying data device, but just remove the mapping within the thin provisioning target. Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/thin-provisioning.txt | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt index 310c120..3370bc4 100644 --- a/Documentation/device-mapper/thin-provisioning.txt +++ b/Documentation/device-mapper/thin-provisioning.txt @@ -223,7 +223,13 @@ i) Constructor [ []*] Optional feature arguments: - - 'skip_block_zeroing': skips the zeroing of newly-provisioned blocks. + + skip_block_zeroing: Skip the zeroing of newly-provisioned blocks. + + ignore_discard: Disable discard support. + + no_discard_passdown: Don't pass discards down to the underlying + data device, but just remove the mapping. Data block size must be between 64KB (128 sectors) and 1GB (2097152 sectors) inclusive. -- cgit v1.1 From a4ffc152198efba2ed9e6eac0eb97f17bfebce85 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Wed, 28 Mar 2012 18:43:38 +0100 Subject: dm: add verity target This device-mapper target creates a read-only device that transparently validates the data on one underlying device against a pre-generated tree of cryptographic checksums stored on a second device. Two checksum device formats are supported: version 0 which is already shipping in Chromium OS and version 1 which incorporates some improvements. Signed-off-by: Mikulas Patocka Signed-off-by: Mandeep Singh Baines Signed-off-by: Will Drewry Signed-off-by: Elly Jones Cc: Milan Broz Cc: Olof Johansson Cc: Steffen Klassert Cc: Andrew Morton Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/verity.txt | 194 +++++++++++++++++++++++++++++++++ 1 file changed, 194 insertions(+) create mode 100644 Documentation/device-mapper/verity.txt (limited to 'Documentation') diff --git a/Documentation/device-mapper/verity.txt b/Documentation/device-mapper/verity.txt new file mode 100644 index 0000000..32e4879 --- /dev/null +++ b/Documentation/device-mapper/verity.txt @@ -0,0 +1,194 @@ +dm-verity +========== + +Device-Mapper's "verity" target provides transparent integrity checking of +block devices using a cryptographic digest provided by the kernel crypto API. +This target is read-only. + +Construction Parameters +======================= + + + + + + + This is the version number of the on-disk format. + + 0 is the original format used in the Chromium OS. + The salt is appended when hashing, digests are stored continuously and + the rest of the block is padded with zeros. + + 1 is the current format that should be used for new devices. + The salt is prepended when hashing and each digest is + padded with zeros to the power of two. + + + This is the device containing the data the integrity of which needs to be + checked. It may be specified as a path, like /dev/sdaX, or a device number, + :. + + + This is the device that that supplies the hash tree data. It may be + specified similarly to the device path and may be the same device. If the + same device is used, the hash_start should be outside of the dm-verity + configured device size. + + + The block size on a data device. Each block corresponds to one digest on + the hash device. + + + The size of a hash block. + + + The number of data blocks on the data device. Additional blocks are + inaccessible. You can place hashes to the same partition as data, in this + case hashes are placed after . + + + This is the offset, in -blocks, from the start of hash_dev + to the root block of the hash tree. + + + The cryptographic hash algorithm used for this device. This should + be the name of the algorithm, like "sha1". + + + The hexadecimal encoding of the cryptographic hash of the root hash block + and the salt. This hash should be trusted as there is no other authenticity + beyond this point. + + + The hexadecimal encoding of the salt value. + +Theory of operation +=================== + +dm-verity is meant to be setup as part of a verified boot path. This +may be anything ranging from a boot using tboot or trustedgrub to just +booting from a known-good device (like a USB drive or CD). + +When a dm-verity device is configured, it is expected that the caller +has been authenticated in some way (cryptographic signatures, etc). +After instantiation, all hashes will be verified on-demand during +disk access. If they cannot be verified up to the root node of the +tree, the root hash, then the I/O will fail. This should identify +tampering with any data on the device and the hash data. + +Cryptographic hashes are used to assert the integrity of the device on a +per-block basis. This allows for a lightweight hash computation on first read +into the page cache. Block hashes are stored linearly-aligned to the nearest +block the size of a page. + +Hash Tree +--------- + +Each node in the tree is a cryptographic hash. If it is a leaf node, the hash +is of some block data on disk. If it is an intermediary node, then the hash is +of a number of child nodes. + +Each entry in the tree is a collection of neighboring nodes that fit in one +block. The number is determined based on block_size and the size of the +selected cryptographic digest algorithm. The hashes are linearly-ordered in +this entry and any unaligned trailing space is ignored but included when +calculating the parent node. + +The tree looks something like: + +alg = sha256, num_blocks = 32768, block_size = 4096 + + [ root ] + / . . . \ + [entry_0] [entry_1] + / . . . \ . . . \ + [entry_0_0] . . . [entry_0_127] . . . . [entry_1_127] + / ... \ / . . . \ / \ + blk_0 ... blk_127 blk_16256 blk_16383 blk_32640 . . . blk_32767 + + +On-disk format +============== + +Below is the recommended on-disk format. The verity kernel code does not +read the on-disk header. It only reads the hash blocks which directly +follow the header. It is expected that a user-space tool will verify the +integrity of the verity_header and then call dmsetup with the correct +parameters. Alternatively, the header can be omitted and the dmsetup +parameters can be passed via the kernel command-line in a rooted chain +of trust where the command-line is verified. + +The on-disk format is especially useful in cases where the hash blocks +are on a separate partition. The magic number allows easy identification +of the partition contents. Alternatively, the hash blocks can be stored +in the same partition as the data to be verified. In such a configuration +the filesystem on the partition would be sized a little smaller than +the full-partition, leaving room for the hash blocks. + +struct superblock { + uint8_t signature[8] + "verity\0\0"; + + uint8_t version; + 1 - current format + + uint8_t data_block_bits; + log2(data block size) + + uint8_t hash_block_bits; + log2(hash block size) + + uint8_t pad1[1]; + zero padding + + uint16_t salt_size; + big-endian salt size + + uint8_t pad2[2]; + zero padding + + uint32_t data_blocks_hi; + big-endian high 32 bits of the 64-bit number of data blocks + + uint32_t data_blocks_lo; + big-endian low 32 bits of the 64-bit number of data blocks + + uint8_t algorithm[16]; + cryptographic algorithm + + uint8_t salt[384]; + salt (the salt size is specified above) + + uint8_t pad3[88]; + zero padding to 512-byte boundary +} + +Directly following the header (and with sector number padded to the next hash +block boundary) are the hash blocks which are stored a depth at a time +(starting from the root), sorted in order of increasing index. + +Status +====== +V (for Valid) is returned if every check performed so far was valid. +If any check failed, C (for Corruption) is returned. + +Example +======= + +Setup a device: + dmsetup create vroot --table \ + "0 2097152 "\ + "verity 1 /dev/sda1 /dev/sda2 4096 4096 2097152 1 "\ + "4392712ba01368efdf14b05c76f9e4df0d53664630b5d48632ed17a137f39076 "\ + "1234000000000000000000000000000000000000000000000000000000000000" + +A command line tool veritysetup is available to compute or verify +the hash tree or activate the kernel driver. This is available from +the LVM2 upstream repository and may be supplied as a package called +device-mapper-verity-tools: + git://sources.redhat.com/git/lvm2 + http://sourceware.org/git/?p=lvm2.git + http://sourceware.org/cgi-bin/cvsweb.cgi/LVM2/verity?cvsroot=lvm2 + +veritysetup -a vroot /dev/sda1 /dev/sda2 \ + 4392712ba01368efdf14b05c76f9e4df0d53664630b5d48632ed17a137f39076 -- cgit v1.1