[gparted] Prevent GParted probe starting stopped bcache (#183)

[Mike Fleetwood <mfleetwo src gnome org>]

commit 8640f91a4f4350bf9508a810cbb2ae28a9acb9b2
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Jan 8 12:02:03 2022 +0000

    Prevent GParted probe starting stopped bcache (#183)
    
    From the setup in the previous commit, unregister (stop) all of the
    bcache backing and cache devices.
        # bcache unregister /dev/sdb2
        # bcache unregister /dev/sdb1
        # bcache unregister /dev/sdc1
        # bcache show
        Name        Type        State            Bname       AttachToDev
        /dev/sdb2   1 (data)    inactive         Non-Exist   Alone
        /dev/sdb1   1 (data)    inactive         Non-Exist   Alone
        /dev/sdc1   3 (cache)   inactive         N/A         N/A
    
    Run GParted.  Just the device scanning causes the stopped bcache devices
    to be restarted.
        # bcache show
        Name        Type        State            Bname       AttachToDev
        /dev/sdb2   1 (data)    clean(running)   bcache1     /dev/sdc1
        /dev/sdb1   1 (data)    clean(running)   bcache0     /dev/sdc1
        /dev/sdc1   3 (cache)   active           N/A         N/A
    
    This is nothing new with this patchset, but as a result of existing udev
    behaviour.  The chain of events goes like this:
    
    1. GParted calls ped_device_get() on each whole device;
    2. Libparted opens each partition read-write to flush the cache;
    3. When each is closed the kernel emits a block change event;
    4. Udev fires block rules to detect the possibly changed content;
    5. Udev fires bcache register (AKA start) rule.
    
    More details with the help of udevadm monitor, strace and syslog:
        GParted  | set_devices_thread()
        GParted  |   ped_device_get("/dev/sdb")
        Libparted|     ...
        Libparted|     openat(AT_FDCWD, "/dev/sdb1", O_WRONLY) = 9
        Libparted|     ioctl(9, BLKFLSBUF)        = 0
        Libparted|     close(9)
        KERNEL   | change   /devices/.../block/sdb/sdb1 (block)
        KERNEL   | add      /devices/virtual/bdi/250:0 (bdi)
        KERNEL   | add      /devices/virtual/block/bcache0 (block)
        KERNEL   | change   /devices/virtual/block/bcache0 (block)
        UDEV     | change   /devices/.../block/sdb/sdb1 (block)
        UDEV     | add      /devices/virtual/bdi/250:0 (bdi)
        UDEV     | add      /devices/virtual/block/bcache0 (block)
        UDEV     | change   /devices/virtual/block/bcache0 (block)
        SYSLOG   | kernel: bcache: register_bdev() registered backing device sdb1
    
        # grep bcache-register /lib/udev/rules.d/69-bcache.rules
        RUN+="bcache-register $tempnode"
    
    Fix this by temporarily adding a blank udev override rule to suppress
    automatic starting of bcache devices, just as was previously done for
    Linux Software RAID arrays [1].
    
    [1] a255abf3432ad106fac9c766f0816ada20be8e42
        Prevent GParted starting stopped Linux Software RAID arrays (#709640)
    
    Closes #183 - Basic support for bcache

 gparted.in | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)
---
diff --git a/gparted.in b/gparted.in
index f446d150..3cefc2e3 100755
--- a/gparted.in
+++ b/gparted.in
@@ -176,7 +176,7 @@ fi
 
 #
 # Create temporary blank overrides for all udev rules which automatically
-# start Linux Software RAID array members.
+# start Linux Software RAID array members and Bcache devices.
 #
 # Udev stores volatile / temporary runtime rules in directory /run/udev/rules.d.
 # Older versions use /dev/.udev/rules.d instead, and even older versions don't
@@ -189,16 +189,17 @@ fi
 # found in 64-md-raid.rules and/or 65-md-incremental.rules, depending on the
 # distribution and age.  The rules may be commented out or not exist at all.
 #
-UDEV_TEMP_MDADM_RULES=''  # List of temporary override rules files.
+UDEV_TEMP_RULES=''  # List of temporary override rules files.
 for udev_temp_d in /run/udev /dev/.udev; do
        if test -d "$udev_temp_d"; then
                test ! -d "$udev_temp_d/rules.d" && mkdir "$udev_temp_d/rules.d"
                udev_mdadm_rules=`egrep -l '^[^#].*mdadm (-I|--incremental)' /lib/udev/rules.d/*.rules 2> 
/dev/null`
-               UDEV_TEMP_MDADM_RULES=`echo "$udev_mdadm_rules" | sed 's,^/lib/udev,'"$udev_temp_d"','`
+               udev_bcache_rules=`ls /lib/udev/rules.d/*bcache*.rules 2> /dev/null`
+               UDEV_TEMP_RULES=`echo $udev_mdadm_rules $udev_bcache_rules | sed 's,/lib/udev,/run/udev,g'`
                break
        fi
 done
-for rule in $UDEV_TEMP_MDADM_RULES; do
+for rule in $UDEV_TEMP_RULES; do
        touch "$rule"
 done
 
@@ -228,9 +229,9 @@ status=$?
 
 #
 # Clear any temporary override udev rules used to stop udev automatically
-# starting Linux Software RAID array members.
+# starting Linux Software RAID array members and Bcache devices.
 #
-for rule in $UDEV_TEMP_MDADM_RULES; do
+for rule in $UDEV_TEMP_RULES; do
        rm -f "$rule"
 done