Update on TRIM support

[Tim Bisson <bissont@xxxxxxx>]

Hi All,

Here's an update on TRIM support based on feedback from Matt, Alex, 
Venkatesh, and others. Thanks guys.

First, the code:
https://github.com/bissont/DragonFlyBSD

If you clone the code and do a:
git difftool upstream/master..HEAD
you can get a diff against the current master (as of today).

Changes:
* Moved the underlying TRIM code from the IDE driver to the AHCI/SCSI 
driver.
* Made UFS block frees (ffs_blkfree()) execute TRIM command on blocks 
asynchronously instead of synchronously. Once the TRIM command is 
completed, we free the actual blocks in the freemap in the callback. 
This makes delete performance much faster as we don't have to wait for 
the TRIM command to finish before returning from the ffs_blkfree().
* Added an option, -E to newfs_hammer, that will run TRIM on the devices 
making up the hammer file system before the hammer file system is created.
* Modified the IOCTL to take in bytes rather than sectors. In the IOCTL, 
we  issue a BUF_CMD_FREEBLKS command using a struct buf, which has a 
size limit of 2^31 (b_bcount) bytes. Therefore, we potentially have to 
break up the IOCTL TRIM command into multiple requests if the original 
command is for more than 2^31 bytes in size.

From "man newfs":
-R      Turn on the TRIM enable flag.  If enabled, and if the underlying
             device supports the BIO_DELETE command, the file system 
will send
             a delete request to the underlying device for each freed 
block.
             The trim enable flag is typically set when the underlying 
device
             uses flash-memory as the device can use the delete command to
             pre-zero or at least avoid copying blocks that have been 
deleted.

-E      Use TRIM to erase the file system before creating it.  If used
             and the underlying device supports TRIM, the device's LBAs 
will
             be erased using the TRIM command before the file system is 
cre-
             ated.

From "man newfs_hammer"
-E      TRIM Device(s) before FS creation. Should only be called if all
             devices are SSDs that support TRIM.


Any suggestions, ideas, or feedback is welcome.

Thanks,
Tim