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]>

7 files changed, 14 insertions, 0 deletions

diff --git a/include/Makefile.in b/include/Makefile.in
index d7423a3c7..9f3972782 100644
--- a/include/Makefile.in
+++ b/include/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/include/linux/Makefile.in b/include/linux/Makefile.in
index d18e5dd9c..9c69b6257 100644
--- a/include/linux/Makefile.in
+++ b/include/linux/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/include/linux/blkdev_compat.h b/include/linux/blkdev_compat.h
index 56a1bafe9..bd1b2bf54 100644
--- a/include/linux/blkdev_compat.h
+++ b/include/linux/blkdev_compat.h
@@ -425,6 +425,14 @@ bio_set_flags_failfast(struct block_device *bdev, int *flags)
 #endif
 
 /*
+ * 2.6.32 API change
+ * Use the normal I/O patch for discards.
+ */
+#ifdef REQ_DISCARD
+# define VDEV_REQ_DISCARD		REQ_DISCARD
+#endif
+
+/*
  * Default Linux IO Scheduler,
  * Setting the scheduler to noop will allow the Linux IO scheduler to
  * still perform front and back merging, while leaving the request
diff --git a/include/sys/Makefile.in b/include/sys/Makefile.in
index 06c20479b..91fd34b65 100644
--- a/include/sys/Makefile.in
+++ b/include/sys/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/include/sys/fm/Makefile.in b/include/sys/fm/Makefile.in
index 245995dda..0dcd27b10 100644
--- a/include/sys/fm/Makefile.in
+++ b/include/sys/fm/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/include/sys/fm/fs/Makefile.in b/include/sys/fm/fs/Makefile.in
index 10dcd83e9..03c32de06 100644
--- a/include/sys/fm/fs/Makefile.in
+++ b/include/sys/fm/fs/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/include/sys/fs/Makefile.in b/include/sys/fs/Makefile.in
index ee2f16821..1f8de0f07 100644
--- a/include/sys/fs/Makefile.in
+++ b/include/sys/fs/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 \