[PATCH v8 8/9] qemu-binfmt-conf.sh: add option --clear

[Unai Martinez-Corral <unai.martinezcorral@ehu.eus>]

This is a partial implementation.

Allows to remove a single or a list of already registered binfmt
interpreters. Valid values are those in qemu_target_list.
If TARGETS is empty, all the existing 'qemu-*' interpreters are
removed.

This is partial because 'debian' and 'systemd' configurations are not
supported. The script will exit with error 'option clear not
implemented for this mode yet'.

Removal is done by printing '-1' as explained at:
https://www.kernel.org/doc/Documentation/admin-guide/binfmt-misc.rst

Signed-off-by: Unai Martinez-Corral <unai.martinezcorral@ehu.eus>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
---
 scripts/qemu-binfmt-conf.sh | 36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/scripts/qemu-binfmt-conf.sh b/scripts/qemu-binfmt-conf.sh
index d5d3484b58..9685456747 100755
--- a/scripts/qemu-binfmt-conf.sh
+++ b/scripts/qemu-binfmt-conf.sh
@@ -201,7 +201,7 @@ Options and associated environment variables:
 
 Argument             Env-variable     Description
 TARGETS              QEMU_TARGETS     A single arch name or a list of them (see all names below);
-                                      if empty, configure all known targets;
+                                      if empty, configure/clear all known targets;
                                       if 'NONE', no interpreter is configured.
 -h|--help                             display this usage
 -Q|--path PATH       QEMU_PATH        set path to qemu interpreter(s)
@@ -210,6 +210,8 @@ TARGETS              QEMU_TARGETS     A single arch name or a list of them (see
                                       uses are cloned from the open file.
 -c|--credential      QEMU_CREDENTIAL  (yes) credential and security tokens are calculated according
                                       to the binary to interpret
+-r|--clear           QEMU_CLEAR       (yes) remove registered interpreters for target TARGETS;
+                                      then exit.
 -e|--exportdir PATH                   define where to write configuration files
                                       (default: $SYSTEMDDIR or $DEBIANDIR)
 -s|--systemd                          don't write into /proc, generate file(s) for
@@ -222,6 +224,7 @@ QEMU_PATH=$QEMU_PATH
 QEMU_SUFFIX=$QEMU_SUFFIX
 QEMU_PERSISTENT=$QEMU_PERSISTENT
 QEMU_CREDENTIAL=$QEMU_CREDENTIAL
+QEMU_CLEAR=$QEMU_CLEAR
 
 To import templates with update-binfmts, use :
 
@@ -348,8 +351,22 @@ qemu_set_binfmts() {
     done
 }
 
+qemu_clear_notimplemented() {
+    echo "ERROR: option clear not implemented for this mode yet" 1>&2
+    usage
+    exit 1
+}
+
+qemu_clear_interpreter() {
+    p="/proc/sys/fs/binfmt_misc/$1"
+    if [ -f "$p" ] ; then
+      printf %s -1 > "$p"
+    fi
+}
+
 CHECK=qemu_check_bintfmt_misc
 BINFMT_SET=qemu_register_interpreter
+BINFMT_CLEAR=qemu_clear_interpreter
 
 SYSTEMDDIR="/etc/binfmt.d"
 DEBIANDIR="/usr/share/binfmts"
@@ -359,20 +376,26 @@ QEMU_PATH="${QEMU_PATH:-/usr/local/bin}"
 QEMU_SUFFIX="${QEMU_SUFFIX:-}"
 QEMU_PERSISTENT="${QEMU_PERSISTENT:-no}"
 QEMU_CREDENTIAL="${QEMU_CREDENTIAL:-no}"
+QEMU_CLEAR="${QEMU_CLEAR:-no}"
 
-options=$(getopt -o dsQ:S:e:hcp -l debian,systemd,path:,suffix:,exportdir:,help,credential,persistent -- "$@")
+options=$(getopt -o rdsQ:S:e:hcp -l clear,debian,systemd,path:,suffix:,exportdir:,help,credential,persistent -- "$@")
 eval set -- "$options"
 
 while true ; do
     case "$1" in
+    -r|--clear)
+        QEMU_CLEAR="yes"
+        ;;
     -d|--debian)
         CHECK=qemu_check_debian
         BINFMT_SET=qemu_generate_debian
+        BINFMT_CLEAR=qemu_clear_notimplemented
         EXPORTDIR=${EXPORTDIR:-$DEBIANDIR}
         ;;
     -s|--systemd)
         CHECK=qemu_check_systemd
         BINFMT_SET=qemu_generate_systemd
+        BINFMT_CLEAR=qemu_clear_notimplemented
         EXPORTDIR=${EXPORTDIR:-$SYSTEMDDIR}
         ;;
     -Q|--path)
@@ -407,4 +430,13 @@ done
 shift
 
 $CHECK
+
+if [ "x$QEMU_CLEAR" = "xyes" ] ; then
+    qemu_check_target_list "$@"
+    for t in $checked_target_list ; do
+        $BINFMT_CLEAR "qemu-$t"
+    done
+    exit
+fi
+
 qemu_set_binfmts "$@"
-- 
2.25.1