Re: [Qemu-devel] [PATCH v4 2/2] qemu-ga: sample fsfreeze hooks

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 22 Nov 2012 11:15:49 +0900
Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com> wrote:

> Adds sample hook scripts for --fsfreeze-hook option of qemu-ga.
>   - fsfreeze-hook : execute scripts in fsfreeze-hook.d/
>   - fsfreeze-hook.d.sample/mysql-flush.sh : quiesce MySQL before snapshot
> 
> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
> ---
>  docs/qemu-guest-agent/fsfreeze-hook                |   31 +++++++++++++
>  .../fsfreeze-hook.d.sample/mysql-flush.sh          |   47 ++++++++++++++++++++
>  2 files changed, 78 insertions(+)
>  create mode 100755 docs/qemu-guest-agent/fsfreeze-hook
>  create mode 100755 docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
> 
> diff --git a/docs/qemu-guest-agent/fsfreeze-hook b/docs/qemu-guest-agent/fsfreeze-hook
> new file mode 100755
> index 0000000..319f68c
> --- /dev/null
> +++ b/docs/qemu-guest-agent/fsfreeze-hook
> @@ -0,0 +1,31 @@
> +#!/bin/sh
> +
> +# This script is executed when a guest agent receives fsfreeze-freeze and
> +# fsfreeze-thaw command, if it is specified in --fsfreeze-hook (-F)
> +# option of qemu-ga or placed in default path (/etc/qemu/fsfreeze-hook).
> +# When the agent receives fsfreeze-freeze request, this script is issued with
> +# "freeze" argument before the filesystem is freezed. And for fsfreeze-thaw
> +# request, it is issued with "thaw" argument after filesystem is thawed.
> +
> +LOGFILE=/var/log/qga-fsfreeze-hook.log
> +FSFREEZE_D=$(dirname -- "$0")/fsfreeze-hook.d
> +
> +# Check whether file $1 is a backup or rpm-generated file and should be ignored
> +is_ignored_file() {
> +    case "$1" in
> +        *~ | *.bak | *.orig | *.rpmnew | *.rpmorig | *.rpmsave)
> +            return 0 ;;
> +    esac
> +    return 1
> +}
> +
> +# Iterate executables in directory "fsfreeze-hook.d" with the specified args
> +[ ! -d "$FSFREEZE_D" ] && exit 1
> +for file in "$FSFREEZE_D"/* ; do
> +    is_ignored_file "$file" && continue
> +    [ -x "$file" ] || continue
> +    echo "$(date): execute $file $@" >>$LOGFILE
> +    "$file" "$@" >>$LOGFILE 2>&1
> +    STATUS=$?
> +    echo "$(date): $file finished with status=$STATUS" >>$LOGFILE
> +done

execute_fsfreeze_hook() will fail the freeze process if this script fails. Two
comments:

 1. Do we want to fail the freeze process if one of the sub-scripts fails?
    If yes, then we have to exit 1 in the first failure

 2. The exit status of the script will echo's exit status. I doubt we want that

> diff --git a/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh b/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
> new file mode 100755
> index 0000000..e6d7998
> --- /dev/null
> +++ b/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
> @@ -0,0 +1,47 @@
> +#!/bin/sh
> +
> +# Flush MySQL tables to the disk before the filesystem is freezed.
> +# At the same time, this keeps a read lock while the filesystem is freezed
> +# in order to avoid write accesses by the other clients.
> +
> +MYSQL="mysql -uroot" #"-prootpassword"
> +FIFO=/tmp/mysql-flush.fifo
> +
> +flush_and_wait() {
> +    printf "FLUSH TABLES WITH READ LOCK \\G\n"
> +    read < $FIFO
> +    printf "UNLOCK TABLES \\G\n"
> +}
> +
> +case "$1" in
> +    freeze)
> +        mkfifo $FIFO || exit 1
> +        flush_and_wait | $MYSQL &

Honest question: what happens if I don't have mysql installed?

> +        # wait until every block is flushed
> +        while [ "$(echo 'SHOW STATUS LIKE "Key_blocks_not_flushed"' |\
> +                 $MYSQL | tail -1 | cut -f 2)" -gt 0 ]; do
> +            sleep 1
> +        done
> +        # for InnoDB, wait until every log is flushed
> +        INNODB_STATUS=$(mktemp /tmp/mysql-flush.XXXXXX)
> +        [ $? -ne 0 ] && exit 2
> +        trap "rm -f $INNODB_STATUS" SIGINT
> +        while :; do
> +            printf "SHOW ENGINE INNODB STATUS \\G" | $MYSQL > $INNODB_STATUS
> +            LOG_CURRENT=$(grep 'Log sequence number' $INNODB_STATUS |\
> +                          tr -s ' ' | cut -d' ' -f4)
> +            LOG_FLUSHED=$(grep 'Log flushed up to' $INNODB_STATUS |\
> +                          tr -s ' ' | cut -d' ' -f5)
> +            [ "$LOG_CURRENT" = "$LOG_FLUSHED" ] && break
> +            sleep 1
> +        done
> +        rm -f $INNODB_STATUS
> +        ;;
> +
> +    thaw)
> +        [ ! -p $FIFO ] && exit 1
> +        echo > $FIFO
> +        rm -f $FIFO
> +        ;;
> +esac
> +
> 
>