On Sat, Nov 02, 2013 at 07:45:30PM -0400, Theodore Ts'o wrote: > Add the ability for a user who has write access to a file to issue a > discard request for blocks belonging to a file. This can be done via > a new flag to the FIEMAP ioctl, or via the BLKDISCARD ioctl (which > previously only worked on block devices). > > Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx> FIEMAP is not the correct interface for data modifying operations. It is an interface that returns information about file metadata (i.e the layout of a file) - it is not an interface for modifying the contents of the file. fallocate() is the interface used to modify file layout and manipulate the data within it and hence, IMO, is much better aligned to this operation. And to tell the truth, I'd much prefer such an interface is guaranteed to return zeros to users rather than rely on whether the underlying device supports discard or whatever they return after a discard. i.e. if the user is asking to destroy the data in the file, we better be able to ensure the data in the file is in a known state at the filesystem level regardless of the underlying storage capabilities.... For example, XFS already has a XFS_IOC_ZERO operation which is used to return allocated blocks to unwritten state (i.e. always return zeros) and could easily be extended to issue discards on the blocks if the underlying device supports discards-to-zero or WRITE_SAME. I've previously proposed this interface for fallocate() - old patch here: http://permalink.gmane.org/gmane.linux.file-systems/62449 Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
