New flag to super block for IMA

["Kasatkin, Dmitry" <dmitry.kasatkin@intel.com>]

Hello Al,

Certain file system types and partitions will never be measured or
appraised depending on the IMA policy.
For example, pseudo file systems are not measured and appraised.
In upstream IMA implementation policy will be checked again and again
for every inode in the filesystem.
It happens thousands times per second. That is absolute waste of CPU
and may be batter resources.

To overcome such issue I would like to have a flag in super block data
structure which can be set once if IMA
does not need to measure anything from a partition.. The flag might be
tested by ima hooks to return without doing anything.

I looked to <linux/fs.h> and found that there is a possibility to to
add additional flag for sb->s_flags.
For example

#define MS_NOT_IMA		(1<<25) /* NOT_IMA */
#define IS_I_NOT_IMA(inode)   __IS_FLG(inode, MS_NOT_IMA)


Another way is to add additional dedicated member to the sb structure.

Can you please advice about this?

Thanks,
Dmitry