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SubjectQuestion for remount

Followings are 3 stories of remount cgroup,

1. remount with devices.

# mount -t cgroup none /cgroups -ocpuacct,release_agent=xxx
# echo > /cgroups/release_agent #clear release agent by hand
# mount -t cgroup none /cgroups -oremount,cpuacct
# cat /cgroups/release_agent
=> release_agent is ""
2. remount without devices, mount command will read /proc/mounts and
copies option.

# mount -t cgroup none /cgroups -ocpuacct,release_agent=xxx
# echo > /cgroups/release_agent #clear release agent by hand
# mount /cgroups -oremount,cpuacct #don't specify device
# cat /cgroups/release_agent
=> xxx
Hmm, release_agent is copied from /proc/mounts and release_agent revives.

3. remount without devices, mount command will read /proc/mounts
# mount -t cgroup none /cgroups -ocpuacct,release_agent=xxx
# mount /cgroups -oremount,cpuacct,release_agent=xxx
=> error
"release_agent=" will be found twice and this returns -INVAL

maybe case "2" is not ideal, I think. (but it may not be bug.)

My point is following.

1. Documentation/cgroups/cgroup.txt says
#mount -oremount,cpuset,ns /dev/cgroup
But this should be
#mount -tcgroup none /dev/cgroup -oremount,cpuset,ns

2. /proc/mounts information of release_agent should be updated....
when it's overwritten directly.
3. If "2" is impossible, changing release_agent at remount should not be allowed.

How do you think ?

Thanks,
-Kame



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