Sven Eschenberg wrote:
> Dear List,
>
> is there any convenient way to set a dm-crypts volume readahead value?
> Cryptsetup and the luks metadata seem to lack this option. If one puts a
> dm-crypt volume on a raid, aside from aligning it, the crypted volumes
> readahead should match the stripe size.
> Why does dmcrypt itself not evaluate the current readahead of the
> underlying blockdevice and after creating the mapping applies it to the
> newly created blockdevice?
>
Because the calculation of readahead should be done in userspace and cryptsetup
do not implement it yet. (Readahead setting was not available in old libdevmapper.)
I think this patch should be enough to do that:
(I can commit it to usptream svn if Clemens agrees)
Retain readahead of underlying device.
Signed-off-by: Milan Broz <mbroz@xxxxxxxxxx>
---
lib/libdevmapper.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
Index: cryptsetup.upstream/lib/libdevmapper.c
===================================================================
--- cryptsetup.upstream.orig/lib/libdevmapper.c 2009-06-02 15:35:57.000000000 +0200
+++ cryptsetup.upstream/lib/libdevmapper.c 2009-06-02 16:38:13.000000000 +0200
@@ -6,10 +6,13 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
+#include <sys/ioctl.h>
#include <unistd.h>
#include <dirent.h>
#include <errno.h>
#include <libdevmapper.h>
+#include <fcntl.h>
+#include <linux/fs.h>
#include "libcryptsetup.h"
#include "internal.h"
@@ -111,6 +114,23 @@ static char *lookup_dev(const char *dev)
return __lookup_dev(buf, makedev(major, minor));
}
+static int _dev_read_ahead(const char *dev, uint32_t *read_ahead)
+{
+ int fd, r = 0;
+ long read_ahead_long;
+
+ if ((fd = open(dev, O_RDONLY)) < 0)
+ return 0;
+
+ r = ioctl(fd, BLKRAGET, &read_ahead_long) ? 0 : 1;
+ close(fd);
+
+ if (r)
+ *read_ahead = (uint32_t) read_ahead_long;
+
+ return r;
+}
+
static char *get_params(struct crypt_options *options, const char *key)
{
char *params;
@@ -234,6 +254,7 @@ static int dm_create_device(int reload,
struct dm_info dmi;
char *params = NULL;
int r = -EINVAL;
+ uint32_t read_ahead = 0;
params = get_params(options, key);
if (!params)
@@ -247,6 +268,11 @@ static int dm_create_device(int reload,
goto out;
if (!dm_task_add_target(dmt, 0, options->size, CRYPT_TARGET, params))
goto out;
+
+ if (_dev_read_ahead(options->device, &read_ahead) &&
+ !dm_task_set_read_ahead(dmt, read_ahead, DM_READ_AHEAD_MINIMUM_FLAG))
+ goto out;
+
if (!dm_task_run(dmt))
goto out;
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