zfs_create: round up volume size to multiple of bs

Round up the volume size requested in `zfs create -V size` to the next
higher multiple of the volblocksize. Updates the man page and adds a
test to verify the new behavior.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reported-by: puffi <puffi@users.noreply.github.com>
Signed-off-by: Alex John <alex@stty.io>
Closes #8541 
Closes #10196

cmd/zfs/zfs_main.c

@@ -1038,6 +1038,31 @@ zfs_do_create(int argc, char **argv)
 		}
 	}
 
+	/*
+	 * if volsize is not a multiple of volblocksize, round it up to the
+	 * nearest multiple of the volblocksize
+	 */
+	if (type == ZFS_TYPE_VOLUME) {
+		uint64_t volblocksize;
+
+		if (nvlist_lookup_uint64(props,
+		    zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE),
+		    &volblocksize) != 0)
+			volblocksize = ZVOL_DEFAULT_BLOCKSIZE;
+
+		if (volsize % volblocksize) {
+			volsize = P2ROUNDUP_TYPED(volsize, volblocksize,
+			    uint64_t);
+
+			if (nvlist_add_uint64(props,
+			    zfs_prop_to_name(ZFS_PROP_VOLSIZE), volsize) != 0) {
+				nvlist_free(props);
+				nomem();
+			}
+		}
+	}
+
+
 	if (type == ZFS_TYPE_VOLUME && !noreserve) {
 		uint64_t spa_version;
 		zfs_prop_t resv_prop;

man/man8/zfs-create.8

@@ -143,8 +143,7 @@ The size represents the logical size as exported by the device.
 By default, a reservation of equal size is created.
 .Pp
 .Ar size
-is automatically rounded up to the nearest 128 Kbytes to ensure that the volume
+is automatically rounded up to the nearest multiple of the
-has an integral number of blocks regardless of
 .Sy blocksize .
 .Bl -tag -width "-b"
 .It Fl b Ar blocksize

tests/zfs-tests/tests/functional/cli_root/zfs_create/zfs_create.cfg

@@ -54,6 +54,12 @@ export VOL_LIMIT_KEYWORD1="1TB on 32-bit"
 export VOL_LIMIT_KEYWORD2="value is too large"
 export VOL_LIMIT_KEYWORD3="volume size exceeds limit"
 
-set -A size "8k" "8K" "1m" "1M" "1mb" "1mB" "1Mb" "1MB" "1g" "1G" \
+set -A size "8k" "8K" "35K" "1m" "1M" "1mb" "1mB" "1Mb" "1MB" "1g" "1G" \
 	"1p" "1P" "1z" "1Z" "1gb" "1gB" "1Gb" "1GB" "1pb" "1pB" "1Pb" \
 	"1PB" "1zb" "1zB" "1Zb" "1ZB"
+
+# If a datasize has a volume size that is not a multiple of the blocksize,
+# explicitly check that its size has been rounded up to the nearest multiple
+# The volume with the exact size must exist in the "size" array above
+set -A explicit_size_check "35K"
+set -A expected_rounded_size "40960"

tests/zfs-tests/tests/functional/cli_root/zfs_create/zfs_create_002_pos.ksh

@@ -31,6 +31,7 @@
 
 . $STF_SUITE/include/libtest.shlib
 . $STF_SUITE/tests/functional/cli_root/zfs_create/zfs_create.cfg
+. $STF_SUITE/tests/functional/cli_root/zfs_create/zfs_create_common.kshlib
 
 #
 # DESCRIPTION:
@@ -39,6 +40,8 @@
 # STRATEGY:
 # 1. Create a volume in the storage pool.
 # 2. Verify the volume is created correctly.
+# 3. Verify that the volume created has its volsize rounded to the nearest
+#    multiple of the blocksize (in this case, the default blocksize)
 #
 
 verify_runnable "global"
@@ -76,6 +79,15 @@ while (( $j < ${#size[*]} )); do
 	fi
 
 	((j = j + 1))
-
 done
+
+typeset -i j=0
+while (( $j < ${#explicit_size_check[*]} )); do
+  propertycheck ${TESTPOOL}/${TESTVOL}${explicit_size_check[j]} \
+    volsize=${expected_rounded_size[j]} || \
+    log_fail "volsize ${size[j]} was not rounded up"
+
+	((j = j + 1))
+done
+
 log_pass "'zfs create -s -V <size> <volume>' works as expected."