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

[Jeff Mahoney <jeffm@suse.com>]

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On 5/6/16 3:27 PM, 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.

I did submit this initially to the systemd folks and they said it
belonged in the device-mapper package.  I'm not convinced.
Device-mapper has no business worrying about how to properly tell btrfs
about its friendly names.  We'll leave the debate of why it is that
systemd has any business implementing its own btrfs ready command and
using it to provide a udev rule but NOT this part of it for another day.

-Jeff


> ---
>  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..bbe1c35
> --- /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}=="?*", TEST=="/dev/mapper/$env{DM_NAME}", RUN{builtin}+="btrfs ready /dev/mapper/$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"
> 


-- 
Jeff Mahoney
SUSE Labs


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