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zfs/config/kernel-blk-queue-discard.m4

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Add support for DISCARD to ZVOLs. DISCARD (REQ_DISCARD, BLKDISCARD) is useful for thin provisioning. It allows ZVOL clients to discard (unmap, trim) block ranges from a ZVOL, thus optimizing disk space usage by allowing a ZVOL to shrink instead of just grow. We can't use zfs_space() or zfs_freesp() here, since these functions only work on regular files, not volumes. Fortunately we can use the low-level function dmu_free_long_range() which does exactly what we want. Currently the discard operation is not added to the log. That's not a big deal since losing discard requests cannot result in data corruption. It would however result in disk space usage higher than it should be. Thus adding log support to zvol_discard() is probably a good idea for a future improvement. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2011-09-02 13:23:12 +00:00
dnl #
dnl # 2.6.32 API change
dnl # Discard requests were moved to the normal I/O path.
dnl #
AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_DISCARD], [
AC_MSG_CHECKING([whether blk_queue_discard() is available])
tmp_flags="$EXTRA_KCFLAGS"
Only use gcc -Wunused-but-set-variable when available Certain versions of gcc generate an 'unrecognized command line option' error message when -Wunused-but-set-variable is used unconditionally. This in turn can cause several of the autoconf tests to misdetect an interface. Now, the use of -Wunused-but-set-variable in the autoconf tests was introduced by commit b9c59ec8 to address a gcc 4.6 compatibility problem. So we really only need to pass this option for version of gcc which are known to support it. Therefore, the tests have been updated to use the result of the existing ZFS_AC_CONFIG_ALWAYS_NO_UNUSED_BUT_SET_VARIABLE which determines if gcc supports this option. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1004
2013-01-11 00:09:31 +00:00
EXTRA_KCFLAGS="${NO_UNUSED_BUT_SET_VARIABLE}"
Add support for DISCARD to ZVOLs. DISCARD (REQ_DISCARD, BLKDISCARD) is useful for thin provisioning. It allows ZVOL clients to discard (unmap, trim) block ranges from a ZVOL, thus optimizing disk space usage by allowing a ZVOL to shrink instead of just grow. We can't use zfs_space() or zfs_freesp() here, since these functions only work on regular files, not volumes. Fortunately we can use the low-level function dmu_free_long_range() which does exactly what we want. Currently the discard operation is not added to the log. That's not a big deal since losing discard requests cannot result in data corruption. It would however result in disk space usage higher than it should be. Thus adding log support to zvol_discard() is probably a good idea for a future improvement. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2011-09-02 13:23:12 +00:00
ZFS_LINUX_TRY_COMPILE([
#include <linux/blkdev.h>
],[
struct request_queue *q = NULL;
(void) blk_queue_discard(q);
],[
AC_MSG_RESULT(yes)
AC_DEFINE(HAVE_BLK_QUEUE_DISCARD, 1,
[blk_queue_discard() is available])
],[
AC_MSG_RESULT(no)
])
EXTRA_KCFLAGS="$tmp_flags"
])