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 <[email protected]>

12 files changed, 12 insertions, 0 deletions

diff --git a/cmd/Makefile.in b/cmd/Makefile.in
index 4a38f36fc..b362f4bc4 100644
--- a/cmd/Makefile.in
+++ b/cmd/Makefile.in
@@ -49,6 +49,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/mount_zfs/Makefile.in b/cmd/mount_zfs/Makefile.in
index 273e20542..5945bd1c1 100644
--- a/cmd/mount_zfs/Makefile.in
+++ b/cmd/mount_zfs/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/sas_switch_id/Makefile.in b/cmd/sas_switch_id/Makefile.in
index 73a22c4ef..64d07e09b 100644
--- a/cmd/sas_switch_id/Makefile.in
+++ b/cmd/sas_switch_id/Makefile.in
@@ -51,6 +51,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zdb/Makefile.in b/cmd/zdb/Makefile.in
index 5ce100dd0..0c99ae803 100644
--- a/cmd/zdb/Makefile.in
+++ b/cmd/zdb/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zfs/Makefile.in b/cmd/zfs/Makefile.in
index 81f778a5e..71941603d 100644
--- a/cmd/zfs/Makefile.in
+++ b/cmd/zfs/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zinject/Makefile.in b/cmd/zinject/Makefile.in
index 644c0b2a3..08aaa40ed 100644
--- a/cmd/zinject/Makefile.in
+++ b/cmd/zinject/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zpios/Makefile.in b/cmd/zpios/Makefile.in
index e270f3744..8ab6938cc 100644
--- a/cmd/zpios/Makefile.in
+++ b/cmd/zpios/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zpool/Makefile.in b/cmd/zpool/Makefile.in
index 81620379a..85d09af71 100644
--- a/cmd/zpool/Makefile.in
+++ b/cmd/zpool/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zpool_id/Makefile.in b/cmd/zpool_id/Makefile.in
index 578fdbbc6..204efe831 100644
--- a/cmd/zpool_id/Makefile.in
+++ b/cmd/zpool_id/Makefile.in
@@ -51,6 +51,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zpool_layout/Makefile.in b/cmd/zpool_layout/Makefile.in
index b89e9e8e8..09ed6de1d 100644
--- a/cmd/zpool_layout/Makefile.in
+++ b/cmd/zpool_layout/Makefile.in
@@ -51,6 +51,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/ztest/Makefile.in b/cmd/ztest/Makefile.in
index 70532fbef..f6c5deda7 100644
--- a/cmd/ztest/Makefile.in
+++ b/cmd/ztest/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
diff --git a/cmd/zvol_id/Makefile.in b/cmd/zvol_id/Makefile.in
index 6bacf9944..f369599ee 100644
--- a/cmd/zvol_id/Makefile.in
+++ b/cmd/zvol_id/Makefile.in
@@ -52,6 +52,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-discard.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \