[PATCH 0/2] Fix btrfs support and fix a few bind mount corner cases

[Kairui Song]

Fedora 33 now have btrfs by default, and kdump is failing.

Currently the get_bind_mount_source function won't work with btrfs, and
in fails sone corner cases. This series fixes the issues.

Kairui Song (2):
  Make get_mount_info work with bind mount
  kdump-lib: Fix get_bind_mount_source to support btrfs and fstab

kdump-lib-initramfs.sh |  2 +-
 kdump-lib.sh           | 46 +++++++++++++++++++++++++++---------------
 2 files changed, 31 insertions(+), 17 deletions(-)

[PATCH 1/2] Make get_mount_info work with bind mount

[Kairui Song]

Remove the --real when calling findmnt.

The option is only useful in capture kernel, to avoid
`findmnt` returning the pseudo 'rootfs' for non mounted path.

example, when /kdumproot/mnt/ is not mounted:
kdump:/# findmnt --target /kdumproot/mnt
TARGET SOURCE FSTYPE OPTIONS
/      rootfs rootfs rw,size=61368k,nr_inodes=15342

kdump:/# findmnt --target /kdumproot/mnt
<return 1 and empty output>

But this function will make findmnt also return empty value for bind
mount. So remove it and add an extra if statement for second kernel.
---
 kdump-lib-initramfs.sh | 2 +-
 kdump-lib.sh           | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kdump-lib-initramfs.sh b/kdump-lib-initramfs.sh
index d8d4893..9275c83 100755
--- a/kdump-lib-initramfs.sh
+++ b/kdump-lib-initramfs.sh
@@ -123,7 +123,7 @@ dump_fs()
     ddebug "_mp=$_mp _dev=$_dev _op=$_op"

# If dump path have a corresponding device entry but not mounted, mount it.
-    if [ -n "$_dev" ]; then
+    if [ -n "$_dev" ] && [ "$_dev" != "rootfs" ]; then
         if ! is_mounted "$_mp"; then
             dinfo "dump target $_dev is not mounted, trying to mount..."
             mkdir -p $_mp
diff --git a/kdump-lib.sh b/kdump-lib.sh
index 98ff27c..f04095a 100755
--- a/kdump-lib.sh
+++ b/kdump-lib.sh
@@ -256,9 +256,9 @@ is_mounted()
 get_mount_info()
 {
     local _info_type=$1 _src_type=$2 _src=$3; shift 3
-    local _info=$(findmnt --real -k -n -r -o $_info_type --$_src_type $_src $@)
+    local _info=$(findmnt -k -n -r -o $_info_type --$_src_type $_src $@)

-    [ -z "$_info" ] && [ -e "/etc/fstab" ] && _info=$(findmnt --real -s -n -r -o $_info_type --$_src_type $_src $@)
+    [ -z "$_info" ] && [ -e "/etc/fstab" ] && _info=$(findmnt -s -n -r -o $_info_type --$_src_type $_src $@)

echo $_info
 }

[PATCH 2/2] kdump-lib: Fix get_bind_mount_source to support btrfs and fstab

[Kairui Song]

Currently get_bind_mount_source will not work on btrfs, that's because
this function relies on findmnt to detect bind mount.

For a bind mount, findmnt will return different value with "-v" option.

For example, we have /dev/sdc mounted on /mnt/source, and then bind
mount /mnt/source/sub/path to /mnt/bind:

$ findmnt /mnt/bind
  TARGET    SOURCE              FSTYPE OPTIONS
  /mnt/bind /dev/sdc[/sub/path] ext4   rw,relatime,seclabel

$ findmnt -v /mnt/bind
  TARGET    SOURCE   FSTYPE OPTIONS
  /mnt/bind /dev/sdc ext4   rw,relatime,seclabel

But findmnt also return similiar result for btrfs, on a fresh installed
Fedora 33:

$ findmnt /
  TARGET SOURCE           FSTYPE OPTIONS
  /      /dev/sdb7[/root] btrfs  rw,relatime,seclabel,ssd,space_cache,subvolid=256,subvol=/root

$ findmnt -v /
  TARGET SOURCE    FSTYPE OPTIONS
  /      /dev/sdb7 btrfs  rw,relatime,seclabel,ssd,space_cache,subvolid=256,subvol=/root

The [...] indicator will contain the subvol of btrfs as well. And if
it's bind mounted under btrfs, it will contain a mixup of btrfs subvol
and the actuall fsroot.

And also, if the bind mount source device is not mounted on /,
get_bind_mount_source will also not work.

So rewrite the get_bind_mount_source function, make it work in every
cases.

Tested with:
 - Silverblue's bind mount
 - Bind mount with source device mounted not under /
 - Btrfs
 - Bind mount and source device is Btrfs

Signed-off-by: Kairui Song 
---
 kdump-lib.sh | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/kdump-lib.sh b/kdump-lib.sh
index f04095a..0e38580 100755
--- a/kdump-lib.sh
+++ b/kdump-lib.sh
@@ -211,8 +211,8 @@ get_kdump_targets()
 # /mnt/bind -> /path/to/src, /mnt/bind/dump -> /path/to/src/dump
 #
 # findmnt uses the option "-v, --nofsroot" to exclusive the [/dir]
-# in the SOURCE column for bind-mounts, then if $_mntpoint equals to
-# $_mntpoint_nofsroot, the mountpoint is not bind mounted directory.
+# in the SOURCE column for bind-mounts, then if $_src equals to
+# $_src_nofsroot, the mountpoint is not bind mounted directory.
 #
 # Below is just an example for mount info
 # /dev/mapper/atomicos-root[/ostree/deploy/rhel-atomic-host/var], if the
@@ -220,22 +220,36 @@ get_kdump_targets()
 # part is the bind mounted directory which quotes by bracket "[]".
 get_bind_mount_source()
 {
-    local _path=$1
-    # In case it's a sub path in a mount point, get the mount point first
-    local _mnt_top=$(df $_path | tail -1 | awk '{print $NF}')
-    local _mntpoint=$(findmnt $_mnt_top | tail -n 1 | awk '{print $2}')
-    local _mntpoint_nofsroot=$(findmnt -v $_mnt_top | tail -n 1 | awk '{print $2}')
+    local _mnt=$(df $1 | tail -1 | awk '{print $NF}')
+    local _path=${1#$_mnt}

-    if [[ "$_mntpoint" = $_mntpoint_nofsroot ]]; then
-        echo $_path && return
+    local _src=$(get_mount_info SOURCE target $_mnt -f)
+    local _opt=$(get_mount_info OPTIONS target $_mnt -f)
+    local _fstype=$(get_mount_info FSTYPE target $_mnt -f)
+
+    # bind mount in fstab
+    if [[ -d "$_src" ]] && [[ "$_fstype" = none ]] && (echo "$_opt" | grep -q "\bbind\b"); then
+        echo $_src$_path && return
+    fi
+
+    # direct mount
+    local _src_nofsroot=$(get_mount_info SOURCE target $_mnt -v -f)
+    if [[ $_src_nofsroot = $_src ]]; then
+        echo $_mnt$_path && return
     fi

-    _mntpoint=${_mntpoint#*$_mntpoint_nofsroot}
-    _mntpoint=${_mntpoint#[}
-    _mntpoint=${_mntpoint%]}
-    _path=${_path#$_mnt_top}
+    local _fsroot=${_src#$_src_nofsroot[}
+    _fsroot=${_fsroot%]}
+    _mnt=$(get_mount_info TARGET source $_src_nofsroot -f)

-    echo $_mntpoint$_path
+    # for btrfs, _fsroot will also contain the subvol value as well, strip it
+    if [[ "$_fstype" = btrfs ]]; then
+        local _subvol
+        _subvol=${_opt#*subvol=}
+        _subvol=${_subvol%,*}
+        _fsroot=${_fsroot#$_subvol}
+    fi
+    echo $_mnt$_fsroot$_path
 }

# Return the current underlaying device of a path, ignore bind mounts

[piliu]

On 11/25/2020 06:36 PM, Kairui Song wrote:
> Fedora 33 now have btrfs by default, and kdump is failing.
>
> Currently the get_bind_mount_source function won't work with btrfs, and
> in fails sone corner cases. This series fixes the issues.
>
> Kairui Song (2):
>   Make get_mount_info work with bind mount
>   kdump-lib: Fix get_bind_mount_source to support btrfs and fstab
>
> kdump-lib-initramfs.sh |  2 +-
>  kdump-lib.sh           | 46 +++++++++++++++++++++++++++---------------
>  2 files changed, 31 insertions(+), 17 deletions(-)

For the series,
Acked-by: Pingfan Liu