commit 772ae5f54d69c38a5e3c4352c5fdbdaff141af21 Author: Milan Broz Date: Tue Aug 2 12:32:08 2011 +0100 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 Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/dm-crypt.txt | 21 ++++++++++++- drivers/md/dm-crypt.c | 49 ++++++++++++++++++++++++++++--- 2 files changed, 65 insertions(+), 5 deletions(-) Index: rhel6-compile/Documentation/device-mapper/dm-crypt.txt =================================================================== --- rhel6-compile.orig/Documentation/device-mapper/dm-crypt.txt 2014-05-10 16:54:58.000000000 +0200 +++ rhel6-compile/Documentation/device-mapper/dm-crypt.txt 2014-05-10 16:55:03.000000000 +0200 @@ -4,7 +4,8 @@ dm-crypt Device-Mapper's "crypt" target provides transparent encryption of block devices using the kernel crypto API. -Parameters: +Parameters: \ + [<#opt_params> ] Encryption cipher and an optional IV generation mode. @@ -37,6 +38,24 @@ Parameters: < 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 Index: rhel6-compile/drivers/md/dm-crypt.c =================================================================== --- rhel6-compile.orig/drivers/md/dm-crypt.c 2014-05-10 16:54:59.000000000 +0200 +++ rhel6-compile/drivers/md/dm-crypt.c 2014-05-10 16:55:03.000000000 +0200 @@ -1388,11 +1388,17 @@ bad_mem: static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv) { struct crypt_config *cc; - unsigned int key_size; + unsigned int key_size, opt_params; unsigned long long tmpll; int ret; + struct dm_arg_set as; + const char *opt_string; - if (argc != 5) { + static struct dm_arg _args[] = { + {0, 1, "Invalid number of feature args"}, + }; + + if (argc < 5) { ti->error = "Not enough arguments"; return -EINVAL; } @@ -1461,6 +1467,30 @@ static int crypt_ctr(struct dm_target *t } cc->start = tmpll; + argv += 5; + argc -= 5; + + /* Optional parameters */ + if (argc) { + as.argc = argc; + as.argv = argv; + + ret = dm_read_arg_group(_args, &as, &opt_params, &ti->error); + if (ret) + goto bad; + + opt_string = dm_shift_arg(&as); + + if (opt_params == 1 && opt_string && + !strcasecmp(opt_string, "allow_discards")) + ti->num_discard_requests = 1; + else if (opt_params) { + ret = -EINVAL; + ti->error = "Invalid feature arguments"; + goto bad; + } + } + ret = -ENOMEM; cc->io_queue = create_workqueue("kcryptd_io"); if (!cc->io_queue) { @@ -1488,9 +1518,16 @@ static int crypt_map(struct dm_target *t struct dm_crypt_io *io; struct crypt_config *cc; - if (bio->bi_rw & BIO_FLUSH) { + /* + * If bio is REQ_FLUSH or REQ_DISCARD, just bypass crypt queues. + * - for REQ_FLUSH device-mapper core ensures that no IO is in-flight + * - for REQ_DISCARD caller must use flush if IO ordering matters + */ + if (unlikely(bio->bi_rw & (BIO_FLUSH | BIO_DISCARD))) { cc = ti->private; bio->bi_bdev = cc->dev->bdev; + if (bio_sectors(bio)) + bio->bi_sector = cc->start + dm_target_offset(ti, bio->bi_sector); return DM_MAPIO_REMAPPED; } @@ -1533,6 +1570,10 @@ static int crypt_status(struct dm_target DMEMIT(" %llu %s %llu", (unsigned long long)cc->iv_offset, cc->dev->name, (unsigned long long)cc->start); + + if (ti->num_discard_requests) + DMEMIT(" 1 allow_discards"); + break; } return 0; @@ -1629,7 +1670,7 @@ static int crypt_iterate_devices(struct static struct target_type crypt_target = { .name = "crypt", - .version = {1, 10, 0}, + .version = {1, 11, 0}, .module = THIS_MODULE, .ctr = crypt_ctr, .dtr = crypt_dtr,