On Fri, Jan 31, 2014 at 12:38:22AM -0500, Theodore Ts'o wrote:
> /*
> * Note: this structure is 24 bytes. Using 256 MB zones, an 8TB drive
> * will have 32,768 zones. That means if we tried to use a contiguous
> * array we would need to allocate 768k of contiguous, non-swappable
> * kernel memory. (Boo, hiss.)
> *
> * This large enough that it would be painful to hang an array off the
> * block_device structure. So we will define a function
> * blkdev_query_zones() to selectively return information for some
> * number of zones.
> */
> struct zone_status {
> sector_t z_start;
> __u32 z_length;
> __u32 z_write_ptr_offset; /* offset */
> __u32 z_checkpoint_offset; /* offset */
> __u32 z_flags; /* full, ro, offline, reset_requested */
> };
>
> /*
> * Query the block_device bdev for information about the zones
> * starting at start_sector that match the criteria specified by
> * free_sectors_criteria. Zone status information for at most
> * max_zones will be placed into the memory array ret_zones. The
> * return value contains the number of zones actually returned.
> *
> * If free_sectors_criteria is positive, then return zones that have
> * at least that many sectors available to be written. If it is zero,
> * then match all zones. If free_sectors_criteria is negative, then
> * return the zones that match the following criteria:
> *
> * -1 Return all read-only zones
> * -2 Return all offline zones
> * -3 Return all zones where the write ptr != the checkpoint ptr
> */
> extern int blkdev_query_zones(struct block_device *bdev,
> sector_t start_sector,
> int free_sectors_criteria,
> struct zone_status *ret_zones,
> int max_zones);
So the caller does:
zones = kmalloc(max * sizeof *zones, GFP_KERNEL);
blkdev_query_zones(bdev, sector, fsc, zones, max);
...
kfree(zones);
Just want to be sure I understand the lifetime rules on the memory used.
I imagine the block layer will have some kind of compressed representation,
probably a tree of some kind, then expand that representation into the
zone_status.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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