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authorMilan Broz2011-08-02 12:32:08 +0100
committerAlasdair G Kergon2011-08-02 12:32:08 +0100
commit772ae5f54d69c38a5e3c4352c5fdbdaff141af21 (patch)
tree727b6dc7596b8250d644214695f09e3d6c7e43d1 /Documentation/device-mapper
parent327372797c88b24953f454cd51a3734c02697bdd (diff)
dm crypt: optionally support discard requests
Add optional parameter field to dmcrypt table and support "allow_discards" option. Discard requests bypass crypt queue processing. Bio is simple remapped to underlying device. Note that discard will be never enabled by default because of security consequences. It is up to the administrator to enable it for encrypted devices. (Note that userspace cryptsetup does not understand new optional parameters yet. Support for this will come later. Until then, you should use 'dmsetup' to enable and disable this.) Signed-off-by: Milan Broz <mbroz@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'Documentation/device-mapper')
-rw-r--r--Documentation/device-mapper/dm-crypt.txt21
1 files changed, 20 insertions, 1 deletions
diff --git a/Documentation/device-mapper/dm-crypt.txt b/Documentation/device-mapper/dm-crypt.txt
index 6b5c42dbbe84..2c656ae43ba7 100644
--- a/Documentation/device-mapper/dm-crypt.txt
+++ b/Documentation/device-mapper/dm-crypt.txt
@@ -4,7 +4,8 @@ dm-crypt
Device-Mapper's "crypt" target provides transparent encryption of block devices
using the kernel crypto API.
-Parameters: <cipher> <key> <iv_offset> <device path> <offset>
+Parameters: <cipher> <key> <iv_offset> <device path> \
+ <offset> [<#opt_params> <opt_params>]
<cipher>
Encryption cipher and an optional IV generation mode.
@@ -37,6 +38,24 @@ Parameters: <cipher> <key> <iv_offset> <device path> <offset>
<offset>
Starting sector within the device where the encrypted data begins.
+<#opt_params>
+ Number of optional parameters. If there are no optional parameters,
+ the optional paramaters section can be skipped or #opt_params can be zero.
+ Otherwise #opt_params is the number of following arguments.
+
+ Example of optional parameters section:
+ 1 allow_discards
+
+allow_discards
+ Block discard requests (a.k.a. TRIM) are passed through the crypt device.
+ The default is to ignore discard requests.
+
+ WARNING: Assess the specific security risks carefully before enabling this
+ option. For example, allowing discards on encrypted devices may lead to
+ the leak of information about the ciphertext device (filesystem type,
+ used space etc.) if the discarded blocks can be located easily on the
+ device later.
+
Example scripts
===============
LUKS (Linux Unified Key Setup) is now the preferred way to set up disk