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Chroot: allow multiple simultaneous entry.

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Change enter_chroot.sh to keep a list of open PIDs (enter_chroot.sh
instances) in chroot/var/lock, and use flock on that file to support
atomic operations to it.

When entering chroot, append the PID to the lock file.

When exiting chroot, clear out current PID and any dead
PIDs/duplicates. If the lock file is empty, only then clean up the
mounts.

Note that I have a little bit of code duplication: the number 200,
which is a manually numbered fd in bash, seemed impossible to place
inside a variable. If you know how to do it, please let me know.

Review URL: http://codereview.chromium.org/584010
This commit is contained in:
Andrew de los Reyes 2010-02-10 13:16:36 -08:00
parent b7eb3a2be6
commit c9317eac02
1 changed files with 60 additions and 20 deletions
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80
enter_chroot.sh
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@ -59,33 +59,73 @@ fi
# TODO: replace shflags with something less error-prone, or contribute a fix.
set -e
sudo chmod 0777 "$FLAGS_chroot/var/lock"
LOCKFILE="$FLAGS_chroot/var/lock/enter_chroot"
function setup_env {
echo "Mounting chroot environment."
(
flock 200
echo $$ >> "$LOCKFILE"
# Mount only if not already mounted
MOUNTED_PATH="$(readlink -f "$FLAGS_chroot/proc")"
if [ -z "$(mount | grep -F "on $MOUNTED_PATH")" ]
then
sudo mount none -t proc "$MOUNTED_PATH"
fi
echo "Mounting chroot environment."
MOUNTED_PATH="$(readlink -f "$FLAGS_chroot/dev/pts")"
if [ -z "$(mount | grep -F "on $MOUNTED_PATH")" ]
then
sudo mount none -t devpts "$MOUNTED_PATH"
fi
# Mount only if not already mounted
MOUNTED_PATH="$(readlink -f "$FLAGS_chroot/proc")"
if [ -z "$(mount | grep -F "on $MOUNTED_PATH")" ]
then
sudo mount none -t proc "$MOUNTED_PATH"
fi
MOUNTED_PATH="$(readlink -f "${FLAGS_chroot}$CHROOT_TRUNK_DIR")"
if [ -z "$(mount | grep -F "on $MOUNTED_PATH")" ]
then
sudo mount --bind "$FLAGS_trunk" "$MOUNTED_PATH"
fi
MOUNTED_PATH="$(readlink -f "$FLAGS_chroot/dev/pts")"
if [ -z "$(mount | grep -F "on $MOUNTED_PATH")" ]
then
sudo mount none -t devpts "$MOUNTED_PATH"
fi
MOUNTED_PATH="$(readlink -f "${FLAGS_chroot}$CHROOT_TRUNK_DIR")"
if [ -z "$(mount | grep -F "on $MOUNTED_PATH")" ]
then
sudo mount --bind "$FLAGS_trunk" "$MOUNTED_PATH"
fi
) 200>>"$LOCKFILE"
}
function teardown_env {
echo "Unmounting chroot environment."
mount | grep "on $(readlink -f "$FLAGS_chroot")" | awk '{print $3}' \
| xargs -r -L1 sudo umount
# Only teardown if we're the last enter_chroot to die
(
flock 200
# check each pid in $LOCKFILE to see if it's died unexpectedly
TMP_LOCKFILE="$LOCKFILE.tmp"
echo -n > "$TMP_LOCKFILE" # Erase/reset temp file
cat "$LOCKFILE" | while read PID; do
if [ "$PID" = "$$" ]; then
# ourself, leave PROC_NAME empty
PROC_NAME=""
else
PROC_NAME=$(ps --pid $PID -o comm=)
fi
if [ ! -z "$PROC_NAME" ]; then
# All good, keep going
echo "$PID" >> "$TMP_LOCKFILE"
fi
done
# Remove any dups from lock file while installing new one
sort -n "$TMP_LOCKFILE" | uniq > "$LOCKFILE"
if [ -s "$LOCKFILE" ]; then
echo "At least one other pid is running in the chroot, so not"
echo "tearing down env."
else
echo "Unmounting chroot environment."
mount | grep "on $(readlink -f "$FLAGS_chroot")" | awk '{print $3}' \
| xargs -r -L1 sudo umount
fi
) 200>>"$LOCKFILE"
}
if [ $FLAGS_mount -eq $FLAGS_TRUE ]