[PATCH v2] btrfs-progs: udev: add rules for dm devices

[PATCH v2] btrfs-progs: udev: add rules for dm devices

[Jeff Mahoney]

Systemd's btrfs rule runs btrfs dev ready on each device
as it's discovered.  The btrfs command is executed as a builtin
command via an IMPORT{builtin} rule, which means it gets
executed at rule evaluation time, not rule execution time.  That
means that the device mapper links haven't been setup yet and the only
nodes that can be depended upon are /dev/dm-#.  That we see
/dev/mapper/name names in /proc/mounts is only because we replace the
device name we have cached with the one passed in via mount.  If
we have a multi-device file system and the primary device is removed,
the remaining devices will show /dev/dm-#.  In addition, if the
udev rule is executed again by someone generating a change event (e.g.
partprobe), the names are also replaced by the /dev/dm-# names.

This patch adds a new rule that adds a run rule that calls btrfs dev
ready again using the device mapper links once they're created.
---
 64-btrfs-dm.rules | 10 ++++++++++
 Makefile.in       |  7 +++++++
 configure.ac      |  2 ++
 3 files changed, 19 insertions(+)
 create mode 100644 64-btrfs-dm.rules

diff --git a/64-btrfs-dm.rules b/64-btrfs-dm.rules
new file mode 100644
index 0000000..b2e49f4
--- /dev/null
+++ b/64-btrfs-dm.rules
@@ -0,0 +1,10 @@
+SUBSYSTEM!="block", GOTO="btrfs_end"
+KERNEL!="dm-[0-9]*", GOTO="btrfs_end"
+ACTION!="add|change", GOTO="btrfs_end"
+ENV{ID_FS_TYPE}!="btrfs", GOTO="btrfs_end"
+
+# Once the device mapper symlink is created, tell btrfs about it
+# so we get the friendly name in /proc/mounts (and tools that read it)
+ENV{DM_NAME}=="?*", RUN{builtin}+="btrfs ready /dev/mapper/$env{DM_NAME}"
+
+LABEL="btrfs_end"
diff --git a/Makefile.in b/Makefile.in
index 19697ff..d555f6a 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -83,11 +83,15 @@ libbtrfs_headers = send-stream.h send-utils.h send.h rbtree.h btrfs-list.h \
 	       extent_io.h ioctl.h ctree.h btrfsck.h version.h
 TESTS = fsck-tests.sh convert-tests.sh
 
+udev_rules = 64-btrfs-dm.rules
+
 prefix ?= @prefix@
 exec_prefix = @exec_prefix@
 bindir = @bindir@
 libdir ?= @libdir@
 incdir = @includedir@/btrfs
+udevdir = @UDEVDIR@
+udevruledir = ${udevdir}/rules.d
 
 ifeq ("$(origin V)", "command line")
   BUILD_VERBOSE = $(V)
@@ -377,6 +381,9 @@ install: $(libs) $(progs_install) $(INSTALLDIRS)
 	cp -a $(lib_links) $(DESTDIR)$(libdir)
 	$(INSTALL) -m755 -d $(DESTDIR)$(incdir)
 	$(INSTALL) -m644 $(headers) $(DESTDIR)$(incdir)
+ifneq ($(udevdir), "")
+	$(INSTALL) -m644 $(udev_rules) $(DESTDIR)$(udevruledir)
+endif
 
 install-static: $(progs_static) $(INSTALLDIRS)
 	for p in $(progs_static) ; do \
diff --git a/configure.ac b/configure.ac
index fc343ea..4af7474 100644
--- a/configure.ac
+++ b/configure.ac
@@ -124,6 +124,8 @@ PKG_STATIC(UUID_LIBS_STATIC, [uuid])
 PKG_CHECK_MODULES(ZLIB, [zlib])
 PKG_STATIC(ZLIB_LIBS_STATIC, [zlib])
 
+PKG_CHECK_VAR([UDEVDIR], [udev], [udevdir])
+
 dnl lzo library does not provide pkg-config, let use classic way
 AC_CHECK_LIB([lzo2], [lzo_version], [
 	LZO2_LIBS="-llzo2"
-- 
2.7.1


-- 
Jeff Mahoney
SUSE Labs

Re: [PATCH v2] btrfs-progs: udev: add rules for dm devices

[David Sterba]

On Mon, May 09, 2016 at 11:44:26AM -0400, Jeff Mahoney wrote:
> Systemd's btrfs rule runs btrfs dev ready on each device
> as it's discovered.  The btrfs command is executed as a builtin
> command via an IMPORT{builtin} rule, which means it gets
> executed at rule evaluation time, not rule execution time.  That
> means that the device mapper links haven't been setup yet and the only
> nodes that can be depended upon are /dev/dm-#.  That we see
> /dev/mapper/name names in /proc/mounts is only because we replace the
> device name we have cached with the one passed in via mount.  If
> we have a multi-device file system and the primary device is removed,
> the remaining devices will show /dev/dm-#.  In addition, if the
> udev rule is executed again by someone generating a change event (e.g.
> partprobe), the names are also replaced by the /dev/dm-# names.
> 
> This patch adds a new rule that adds a run rule that calls btrfs dev
> ready again using the device mapper links once they're created.

Applied, thanks.