Use udev to create /dev/zvol/[dataset_name] links

This commit allows zvols with names longer than 32 characters, which
fixes issue on https://github.com/behlendorf/zfs/issues/#issue/102.

Changes include:
- use /dev/zd* device names for zvol, where * is the device minor
  (include/sys/fs/zfs.h, module/zfs/zvol.c).
- add BLKZNAME ioctl to get dataset name from userland
  (include/sys/fs/zfs.h, module/zfs/zvol.c, cmd/zvol_id).
- add udev rule to create /dev/zvol/[dataset_name] and the legacy
  /dev/[dataset_name] symlink. For partitions on zvol, it will create
  /dev/zvol/[dataset_name]-part* (etc/udev/rules.d/60-zvol.rules,
  cmd/zvol_id).

Signed-off-by: Brian Behlendorf <[email protected]>

10 files changed, 761 insertions, 9 deletions

diff --git a/cmd/Makefile.am b/cmd/Makefile.am
index 760854744..af03994ce 100644
--- a/cmd/Makefile.am
+++ b/cmd/Makefile.am
@@ -1 +1 @@
-SUBDIRS = zfs zpool zpool_id zpool_layout zdb zinject ztest zpios
+SUBDIRS = zfs zpool zpool_id zpool_layout zdb zinject ztest zpios zvol_id
diff --git a/cmd/Makefile.in b/cmd/Makefile.in
index f82f9c544..2dcf6a659 100644
--- a/cmd/Makefile.in
+++ b/cmd/Makefile.in
@@ -292,7 +292,7 @@ target_vendor = @target_vendor@
 top_build_prefix = @top_build_prefix@
 top_builddir = @top_builddir@
 top_srcdir = @top_srcdir@
-SUBDIRS = zfs zpool zpool_id zpool_layout zdb zinject ztest zpios
+SUBDIRS = zfs zpool zpool_id zpool_layout zdb zinject ztest zpios zvol_id
 all: all-recursive
 
 .SUFFIXES:
diff --git a/cmd/zvol_id/Makefile.am b/cmd/zvol_id/Makefile.am
new file mode 100644
index 000000000..dcdea58b9
--- /dev/null
+++ b/cmd/zvol_id/Makefile.am
@@ -0,0 +1,10 @@
+include $(top_srcdir)/config/Rules.am
+
+DEFAULT_INCLUDES += \
+	-I$(top_srcdir)/include \
+	-I$(top_srcdir)/lib/libspl/include
+
+bin_PROGRAMS = zvol_id
+
+zvol_id_SOURCES = \
+	$(top_srcdir)/cmd/zvol_id/zvol_id_main.c
diff --git a/cmd/zvol_id/Makefile.in b/cmd/zvol_id/Makefile.in
new file mode 100644
index 000000000..0489034dc
--- /dev/null
+++ b/cmd/zvol_id/Makefile.in
@@ -0,0 +1,634 @@
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+
+zvol_id_main.o: $(top_srcdir)/cmd/zvol_id/zvol_id_main.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT zvol_id_main.o -MD -MP -MF $(DEPDIR)/zvol_id_main.Tpo -c -o zvol_id_main.o `test -f '$(top_srcdir)/cmd/zvol_id/zvol_id_main.c' || echo '$(srcdir)/'`$(top_srcdir)/cmd/zvol_id/zvol_id_main.c
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/zvol_id_main.Tpo $(DEPDIR)/zvol_id_main.Po
+@am__fastdepCC_FALSE@	$(AM_V_CC) @AM_BACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	source='$(top_srcdir)/cmd/zvol_id/zvol_id_main.c' object='zvol_id_main.o' libtool=no @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o zvol_id_main.o `test -f '$(top_srcdir)/cmd/zvol_id/zvol_id_main.c' || echo '$(srcdir)/'`$(top_srcdir)/cmd/zvol_id/zvol_id_main.c
+
+zvol_id_main.obj: $(top_srcdir)/cmd/zvol_id/zvol_id_main.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT zvol_id_main.obj -MD -MP -MF $(DEPDIR)/zvol_id_main.Tpo -c -o zvol_id_main.obj `if test -f '$(top_srcdir)/cmd/zvol_id/zvol_id_main.c'; then $(CYGPATH_W) '$(top_srcdir)/cmd/zvol_id/zvol_id_main.c'; else $(CYGPATH_W) '$(srcdir)/$(top_srcdir)/cmd/zvol_id/zvol_id_main.c'; fi`
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/zvol_id_main.Tpo $(DEPDIR)/zvol_id_main.Po
+@am__fastdepCC_FALSE@	$(AM_V_CC) @AM_BACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	source='$(top_srcdir)/cmd/zvol_id/zvol_id_main.c' object='zvol_id_main.obj' libtool=no @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o zvol_id_main.obj `if test -f '$(top_srcdir)/cmd/zvol_id/zvol_id_main.c'; then $(CYGPATH_W) '$(top_srcdir)/cmd/zvol_id/zvol_id_main.c'; else $(CYGPATH_W) '$(srcdir)/$(top_srcdir)/cmd/zvol_id/zvol_id_main.c'; fi`
+
+mostlyclean-libtool:
+	-rm -f *.lo
+
+clean-libtool:
+	-rm -rf .libs _libs
+
+ID: $(HEADERS) $(SOURCES) $(LISP) $(TAGS_FILES)
+	list='$(SOURCES) $(HEADERS) $(LISP) $(TAGS_FILES)'; \
+	unique=`for i in $$list; do \
+	    if test -f "$$i"; then echo $$i; else echo $(srcdir)/$$i; fi; \
+	  done | \
+	  $(AWK) '{ files[$$0] = 1; nonempty = 1; } \
+	      END { if (nonempty) { for (i in files) print i; }; }'`; \
+	mkid -fID $$unique
+tags: TAGS
+
+TAGS:  $(HEADERS) $(SOURCES)  $(TAGS_DEPENDENCIES) \
+		$(TAGS_FILES) $(LISP)
+	set x; \
+	here=`pwd`; \
+	list='$(SOURCES) $(HEADERS)  $(LISP) $(TAGS_FILES)'; \
+	unique=`for i in $$list; do \
+	    if test -f "$$i"; then echo $$i; else echo $(srcdir)/$$i; fi; \
+	  done | \
+	  $(AWK) '{ files[$$0] = 1; nonempty = 1; } \
+	      END { if (nonempty) { for (i in files) print i; }; }'`; \
+	shift; \
+	if test -z "$(ETAGS_ARGS)$$*$$unique"; then :; else \
+	  test -n "$$unique" || unique=$$empty_fix; \
+	  if test $$# -gt 0; then \
+	    $(ETAGS) $(ETAGSFLAGS) $(AM_ETAGSFLAGS) $(ETAGS_ARGS) \
+	      "$$@" $$unique; \
+	  else \
+	    $(ETAGS) $(ETAGSFLAGS) $(AM_ETAGSFLAGS) $(ETAGS_ARGS) \
+	      $$unique; \
+	  fi; \
+	fi
+ctags: CTAGS
+CTAGS:  $(HEADERS) $(SOURCES)  $(TAGS_DEPENDENCIES) \
+		$(TAGS_FILES) $(LISP)
+	list='$(SOURCES) $(HEADERS)  $(LISP) $(TAGS_FILES)'; \
+	unique=`for i in $$list; do \
+	    if test -f "$$i"; then echo $$i; else echo $(srcdir)/$$i; fi; \
+	  done | \
+	  $(AWK) '{ files[$$0] = 1; nonempty = 1; } \
+	      END { if (nonempty) { for (i in files) print i; }; }'`; \
+	test -z "$(CTAGS_ARGS)$$unique" \
+	  || $(CTAGS) $(CTAGSFLAGS) $(AM_CTAGSFLAGS) $(CTAGS_ARGS) \
+	     $$unique
+
+GTAGS:
+	here=`$(am__cd) $(top_builddir) && pwd` \
+	  && $(am__cd) $(top_srcdir) \
+	  && gtags -i $(GTAGS_ARGS) "$$here"
+
+distclean-tags:
+	-rm -f TAGS ID GTAGS GRTAGS GSYMS GPATH tags
+
+distdir: $(DISTFILES)
+	@srcdirstrip=`echo "$(srcdir)" | sed 's/[].[^$$\\*]/\\\\&/g'`; \
+	topsrcdirstrip=`echo "$(top_srcdir)" | sed 's/[].[^$$\\*]/\\\\&/g'`; \
+	list='$(DISTFILES)'; \
+	  dist_files=`for file in $$list; do echo $$file; done | \
+	  sed -e "s|^$$srcdirstrip/||;t" \
+	      -e "s|^$$topsrcdirstrip/|$(top_builddir)/|;t"`; \
+	case $$dist_files in \
+	  */*) $(MKDIR_P) `echo "$$dist_files" | \
+			   sed '/\//!d;s|^|$(distdir)/|;s,/[^/]*$$,,' | \
+			   sort -u` ;; \
+	esac; \
+	for file in $$dist_files; do \
+	  if test -f $$file || test -d $$file; then d=.; else d=$(srcdir); fi; \
+	  if test -d $$d/$$file; then \
+	    dir=`echo "/$$file" | sed -e 's,/[^/]*$$,,'`; \
+	    if test -d "$(distdir)/$$file"; then \
+	      find "$(distdir)/$$file" -type d ! -perm -700 -exec chmod u+rwx {} \;; \
+	    fi; \
+	    if test -d $(srcdir)/$$file && test $$d != $(srcdir); then \
+	      cp -fpR $(srcdir)/$$file "$(distdir)$$dir" || exit 1; \
+	      find "$(distdir)/$$file" -type d ! -perm -700 -exec chmod u+rwx {} \;; \
+	    fi; \
+	    cp -fpR $$d/$$file "$(distdir)$$dir" || exit 1; \
+	  else \
+	    test -f "$(distdir)/$$file" \
+	    || cp -p $$d/$$file "$(distdir)/$$file" \
+	    || exit 1; \
+	  fi; \
+	done
+check-am: all-am
+check: check-am
+all-am: Makefile $(PROGRAMS)
+installdirs:
+	for dir in "$(DESTDIR)$(bindir)"; do \
+	  test -z "$$dir" || $(MKDIR_P) "$$dir"; \
+	done
+install: install-am
+install-exec: install-exec-am
+install-data: install-data-am
+uninstall: uninstall-am
+
+install-am: all-am
+	@$(MAKE) $(AM_MAKEFLAGS) install-exec-am install-data-am
+
+installcheck: installcheck-am
+install-strip:
+	$(MAKE) $(AM_MAKEFLAGS) INSTALL_PROGRAM="$(INSTALL_STRIP_PROGRAM)" \
+	  install_sh_PROGRAM="$(INSTALL_STRIP_PROGRAM)" INSTALL_STRIP_FLAG=-s \
+	  `test -z '$(STRIP)' || \
+	    echo "INSTALL_PROGRAM_ENV=STRIPPROG='$(STRIP)'"` install
+mostlyclean-generic:
+
+clean-generic:
+
+distclean-generic:
+	-test -z "$(CONFIG_CLEAN_FILES)" || rm -f $(CONFIG_CLEAN_FILES)
+	-test . = "$(srcdir)" || test -z "$(CONFIG_CLEAN_VPATH_FILES)" || rm -f $(CONFIG_CLEAN_VPATH_FILES)
+
+maintainer-clean-generic:
+	@echo "This command is intended for maintainers to use"
+	@echo "it deletes files that may require special tools to rebuild."
+clean: clean-am
+
+clean-am: clean-binPROGRAMS clean-generic clean-libtool mostlyclean-am
+
+distclean: distclean-am
+	-rm -rf ./$(DEPDIR)
+	-rm -f Makefile
+distclean-am: clean-am distclean-compile distclean-generic \
+	distclean-tags
+
+dvi: dvi-am
+
+dvi-am:
+
+html: html-am
+
+html-am:
+
+info: info-am
+
+info-am:
+
+install-data-am:
+
+install-dvi: install-dvi-am
+
+install-dvi-am:
+
+install-exec-am: install-binPROGRAMS
+
+install-html: install-html-am
+
+install-html-am:
+
+install-info: install-info-am
+
+install-info-am:
+
+install-man:
+
+install-pdf: install-pdf-am
+
+install-pdf-am:
+
+install-ps: install-ps-am
+
+install-ps-am:
+
+installcheck-am:
+
+maintainer-clean: maintainer-clean-am
+	-rm -rf ./$(DEPDIR)
+	-rm -f Makefile
+maintainer-clean-am: distclean-am maintainer-clean-generic
+
+mostlyclean: mostlyclean-am
+
+mostlyclean-am: mostlyclean-compile mostlyclean-generic \
+	mostlyclean-libtool
+
+pdf: pdf-am
+
+pdf-am:
+
+ps: ps-am
+
+ps-am:
+
+uninstall-am: uninstall-binPROGRAMS
+
+.MAKE: install-am install-strip
+
+.PHONY: CTAGS GTAGS all all-am check check-am clean clean-binPROGRAMS \
+	clean-generic clean-libtool ctags distclean distclean-compile \
+	distclean-generic distclean-libtool distclean-tags distdir dvi \
+	dvi-am html html-am info info-am install install-am \
+	install-binPROGRAMS install-data install-data-am install-dvi \
+	install-dvi-am install-exec install-exec-am install-html \
+	install-html-am install-info install-info-am install-man \
+	install-pdf install-pdf-am install-ps install-ps-am \
+	install-strip installcheck installcheck-am installdirs \
+	maintainer-clean maintainer-clean-generic mostlyclean \
+	mostlyclean-compile mostlyclean-generic mostlyclean-libtool \
+	pdf pdf-am ps ps-am tags uninstall uninstall-am \
+	uninstall-binPROGRAMS
+
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/cmd/zvol_id/zvol_id_main.c b/cmd/zvol_id/zvol_id_main.c
new file mode 100644
index 000000000..2aa8abbdc
--- /dev/null
+++ b/cmd/zvol_id/zvol_id_main.c
@@ -0,0 +1,90 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (c) 2011, Fajar A. Nugraha.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <linux/ioctl.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <sys/zfs_znode.h>
+#include <sys/fs/zfs.h>
+
+int ioctl_get_msg(char *var, int fd)
+{
+	int error = 0;
+	char msg[ZFS_MAXNAMELEN];
+
+	error = ioctl(fd, BLKZNAME, msg);
+	if (error < 0) {
+		printf("ioctl_get_msg failed:%d\n", error);
+		return (error);
+	}
+
+	snprintf(var, ZFS_MAXNAMELEN, "%s", msg);
+	return (error);
+}
+
+int main(int argc, char **argv)
+{
+	int fd, error = 0;
+	char zvol_name[ZFS_MAXNAMELEN], zvol_name_part[ZFS_MAXNAMELEN];
+	char *dev_name;
+	struct stat64 statbuf;
+	int dev_minor, dev_part;
+
+	if (argc < 2) {
+		printf("Usage: %s /dev/zvol_device_node\n", argv[0]);
+		return (EINVAL);
+	}
+
+	dev_name = argv[1];
+	error = stat64(dev_name, &statbuf);
+	if (error != 0) {
+		printf("Unable to access device file: %s\n", dev_name);
+		return (errno);
+	}
+
+	dev_minor = minor(statbuf.st_rdev);
+	dev_part = dev_minor % ZVOL_MINORS;
+
+	fd = open(dev_name, O_RDONLY);
+	if (fd < 0) {
+		printf("Unable to open device file: %s\n", dev_name);
+		return (errno);
+	}
+
+	ioctl_get_msg(zvol_name, fd);
+	if (dev_part > 0)
+		snprintf(zvol_name_part, ZFS_MAXNAMELEN, "%s-part%d", zvol_name,
+		    dev_part);
+	else
+		snprintf(zvol_name_part, ZFS_MAXNAMELEN, "%s", zvol_name);
+
+	printf("%s\n", zvol_name_part);
+	close(fd);
+	return (error);
+}
diff --git a/configure b/configure
index 60888993b..a9cfbbe1f 100755
--- a/configure
+++ b/configure
@@ -19739,7 +19739,7 @@ fi
 $as_echo "$enable_debug" >&6; }
 
 
-ac_config_files="$ac_config_files Makefile etc/Makefile man/Makefile man/man8/Makefile lib/Makefile lib/libspl/Makefile lib/libspl/asm-generic/Makefile lib/libspl/asm-i386/Makefile lib/libspl/asm-x86_64/Makefile lib/libspl/include/Makefile lib/libspl/include/ia32/Makefile lib/libspl/include/ia32/sys/Makefile lib/libspl/include/rpc/Makefile lib/libspl/include/sys/Makefile lib/libspl/include/sys/sysevent/Makefile lib/libspl/include/sys/dktp/Makefile lib/libspl/include/util/Makefile lib/libavl/Makefile lib/libefi/Makefile lib/libnvpair/Makefile lib/libunicode/Makefile lib/libuutil/Makefile lib/libzpool/Makefile lib/libzfs/Makefile cmd/Makefile cmd/zdb/Makefile cmd/zfs/Makefile cmd/zinject/Makefile cmd/zpool/Makefile cmd/zpool_id/Makefile cmd/zpool_layout/Makefile cmd/ztest/Makefile cmd/zpios/Makefile module/Makefile module/avl/Makefile module/nvpair/Makefile module/unicode/Makefile module/zcommon/Makefile module/zfs/Makefile module/zpios/Makefile include/Makefile include/linux/Makefile include/sys/Makefile include/sys/fs/Makefile include/sys/fm/Makefile include/sys/fm/fs/Makefile scripts/Makefile scripts/zpios-profile/Makefile scripts/zpios-test/Makefile scripts/zpool-config/Makefile scripts/zpool-layout/Makefile scripts/common.sh zfs.spec zfs-modules.spec zfs-script-config.sh"
+ac_config_files="$ac_config_files Makefile etc/Makefile man/Makefile man/man8/Makefile lib/Makefile lib/libspl/Makefile lib/libspl/asm-generic/Makefile lib/libspl/asm-i386/Makefile lib/libspl/asm-x86_64/Makefile lib/libspl/include/Makefile lib/libspl/include/ia32/Makefile lib/libspl/include/ia32/sys/Makefile lib/libspl/include/rpc/Makefile lib/libspl/include/sys/Makefile lib/libspl/include/sys/sysevent/Makefile lib/libspl/include/sys/dktp/Makefile lib/libspl/include/util/Makefile lib/libavl/Makefile lib/libefi/Makefile lib/libnvpair/Makefile lib/libunicode/Makefile lib/libuutil/Makefile lib/libzpool/Makefile lib/libzfs/Makefile cmd/Makefile cmd/zdb/Makefile cmd/zfs/Makefile cmd/zinject/Makefile cmd/zpool/Makefile cmd/zpool_id/Makefile cmd/zpool_layout/Makefile cmd/ztest/Makefile cmd/zpios/Makefile cmd/zvol_id/Makefile module/Makefile module/avl/Makefile module/nvpair/Makefile module/unicode/Makefile module/zcommon/Makefile module/zfs/Makefile module/zpios/Makefile include/Makefile include/linux/Makefile include/sys/Makefile include/sys/fs/Makefile include/sys/fm/Makefile include/sys/fm/fs/Makefile scripts/Makefile scripts/zpios-profile/Makefile scripts/zpios-test/Makefile scripts/zpool-config/Makefile scripts/zpool-layout/Makefile scripts/common.sh zfs.spec zfs-modules.spec zfs-script-config.sh"
 
 
 cat >confcache <<\_ACEOF
@@ -20688,6 +20688,7 @@ do
     "cmd/zpool_layout/Makefile") CONFIG_FILES="$CONFIG_FILES cmd/zpool_layout/Makefile" ;;
     "cmd/ztest/Makefile") CONFIG_FILES="$CONFIG_FILES cmd/ztest/Makefile" ;;
     "cmd/zpios/Makefile") CONFIG_FILES="$CONFIG_FILES cmd/zpios/Makefile" ;;
+    "cmd/zvol_id/Makefile") CONFIG_FILES="$CONFIG_FILES cmd/zvol_id/Makefile" ;;
     "module/Makefile") CONFIG_FILES="$CONFIG_FILES module/Makefile" ;;
     "module/avl/Makefile") CONFIG_FILES="$CONFIG_FILES module/avl/Makefile" ;;
     "module/nvpair/Makefile") CONFIG_FILES="$CONFIG_FILES module/nvpair/Makefile" ;;
diff --git a/configure.ac b/configure.ac
index efebf71e9..abb3ff6ce 100644
--- a/configure.ac
+++ b/configure.ac
@@ -87,6 +87,7 @@ AC_CONFIG_FILES([
 	cmd/zpool_layout/Makefile
 	cmd/ztest/Makefile
 	cmd/zpios/Makefile
+	cmd/zvol_id/Makefile
 	module/Makefile
 	module/avl/Makefile
 	module/nvpair/Makefile
diff --git a/etc/udev/rules.d/60-zvol.rules b/etc/udev/rules.d/60-zvol.rules
new file mode 100644
index 000000000..803d4260d
--- /dev/null
+++ b/etc/udev/rules.d/60-zvol.rules
@@ -0,0 +1,6 @@
+# Peristent links for zvol
+#
+# persistent disk links: /dev/zvol/dataset_name
+# also creates compatibilty symlink of /dev/dataset_name
+
+KERNEL=="zd*" SUBSYSTEM=="block" ACTION=="add" PROGRAM="/usr/bin/zvol_id $tempnode" SYMLINK+="zvol/%c %c"
diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
index 25f256251..44aed1335 100644
--- a/include/sys/fs/zfs.h
+++ b/include/sys/fs/zfs.h
@@ -707,6 +707,7 @@ typedef struct ddt_histogram {
 #define	ZVOL_MINOR_BITS		4
 #define	ZVOL_MINOR_MASK		((1U << ZVOL_MINOR_BITS) - 1)
 #define	ZVOL_MINORS		(1 << 4)
+#define	ZVOL_DEV_NAME		"zd"
 
 #define	ZVOL_PROP_NAME		"name"
 #define	ZVOL_DEFAULT_BLOCKSIZE	8192
@@ -782,6 +783,11 @@ typedef enum zfs_ioc {
 } zfs_ioc_t;
 
 /*
+ * zvol ioctl to get dataset name
+ */
+#define BLKZNAME		_IO(0x12,125)
+
+/*
  * Internal SPA load state.  Used by FMA diagnosis engine.
  */
 typedef enum {
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index e4487f9a6..65a924057 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -58,7 +58,7 @@ static char *zvol_tag = "zvol_tag";
  * The in-core state of each volume.
  */
 typedef struct zvol_state {
-	char			zv_name[DISK_NAME_LEN];	/* name */
+	char			zv_name[MAXNAMELEN];	/* name */
 	uint64_t		zv_volsize;	/* advertised space */
 	uint64_t		zv_volblocksize;/* volume block size */
 	objset_t		*zv_objset;	/* objset handle */
@@ -132,7 +132,7 @@ zvol_find_by_name(const char *name)
 	ASSERT(MUTEX_HELD(&zvol_state_lock));
 	for (zv = list_head(&zvol_state_list); zv != NULL;
 	     zv = list_next(&zvol_state_list, zv)) {
-		if (!strncmp(zv->zv_name, name, DISK_NAME_LEN))
+		if (!strncmp(zv->zv_name, name, MAXNAMELEN))
 			return zv;
 	}
 
@@ -895,6 +895,9 @@ zvol_ioctl(struct block_device *bdev, fmode_t mode,
 	case BLKFLSBUF:
 		zil_commit(zv->zv_zilog, ZVOL_OBJ);
 		break;
+	case BLKZNAME:
+		error = copy_to_user((void *)arg, zv->zv_name, MAXNAMELEN);
+		break;
 
 	default:
 		error = -ENOTTY;
@@ -1058,7 +1061,7 @@ zvol_alloc(dev_t dev, const char *name)
 	zv->zv_queue->queuedata = zv;
 	zv->zv_dev = dev;
 	zv->zv_open_count = 0;
-	strlcpy(zv->zv_name, name, DISK_NAME_LEN);
+	strlcpy(zv->zv_name, name, MAXNAMELEN);
 
 	mutex_init(&zv->zv_znode.z_range_lock, NULL, MUTEX_DEFAULT, NULL);
 	avl_create(&zv->zv_znode.z_range_avl, zfs_range_compare,
@@ -1073,7 +1076,8 @@ zvol_alloc(dev_t dev, const char *name)
 	zv->zv_disk->fops = &zvol_ops;
 	zv->zv_disk->private_data = zv;
 	zv->zv_disk->queue = zv->zv_queue;
-	snprintf(zv->zv_disk->disk_name, DISK_NAME_LEN, "%s", name);
+	snprintf(zv->zv_disk->disk_name, DISK_NAME_LEN, "%s%d",
+	    ZVOL_DEV_NAME, (dev & MINORMASK));
 
 	return zv;
 
@@ -1274,7 +1278,7 @@ zvol_remove_minors(const char *pool)
 	zvol_state_t *zv, *zv_next;
 	char *str;
 
-	str = kmem_zalloc(DISK_NAME_LEN, KM_SLEEP);
+	str = kmem_zalloc(MAXNAMELEN, KM_SLEEP);
 	if (pool) {
 		(void) strncpy(str, pool, strlen(pool));
 		(void) strcat(str, "/");
@@ -1290,7 +1294,7 @@ zvol_remove_minors(const char *pool)
 		}
 	}
 	mutex_exit(&zvol_state_lock);
-	kmem_free(str, DISK_NAME_LEN);
+	kmem_free(str, MAXNAMELEN);
 }
 
 int