On Thu, Mar 3, 2016 at 7:40 PM, Arnd Bergmann arnd@arndb.de wrote:
On Wednesday 02 March 2016 23:50:01 Deepa Dinamani wrote:
/** Assign a default empty range [MAX_VFS_TIME, MIN_VFS_TIME].* This will help VFS detect filesystems that do not populate* these fields in the superblock.*/s->s_time_min = MAX_VFS_TIME;s->s_time_max = MIN_VFS_TIME; s->cleancache_poolid = CLEANCACHE_NO_POOL;I think this is still less clear than it should be, even with the comment explaining it.
As I just replied to Dave, how about initializing both to -1 instead?
This was one of my first ideas. The reason I did not choose this is because 1. [-1, -1] is a valid range theoretically. 2. -1 would now be treated as a value.
It is true that no filesystem is using -1 as a limit. But, I did not feel right excluding a perfectly good value. Choosing [1,1] or any other number except probably 0 would work the same way.
This is the reason that I decided an invalid range should be represented by an invalid tuple and not a single value. My premise was that a range where min_time > max_time is invalid. My first choice here as in the first patch I shared with you privately was [1,-1]. But, the condition min_time < max_time can easily be achieved by changing just one of the values. For instance, [1, 2016]. But, this doesn't necessarily mean that the filesystem explicitly set both the values. For this reason, the invalid range I chose is [max_time, min_time]. Of course [min_time, min_time] and [max_time, max_time] ranges are also considered valid in this approach.
This guarantees 1. That both min and max values are assigned by each filesystem. 2. The range is universally invalid.
-Deepa