> +static int iblock_do_discard(struct se_task *task, enum blk_discard_type type)
> +{
> + struct iblock_dev *ibd = task->se_dev->dev_ptr;
> + struct block_device *bd = ibd->ibd_bd;
> + struct se_cmd *cmd = TASK_CMD(task);
> +
> + if (type == DISCARD_UNMAP)
> + return transport_generic_unmap(cmd, bd);
> + else if (type == DISCARD_WRITE_SAME_UNMAP)
> + return iblock_emulate_write_same_unmap(task);
> + else {
> + printk(KERN_ERR "Unsupported discard_type_t: %d\n", type);
> + return -ENOSYS;
> + }
> +
> + return -ENOSYS;
> +}
> +
I don't think the discard code is quite, nor nicely structured.
The parsing of the WRITE SAME and UNMAP CDBs is something the generic
CDB parsing code should do, and just give a range of lists of lba/len
pairs to the ->discard method in the backed. Also your generic
discard helpers aren't actually generic - they require a block device
and thus should be only in iblock.c. While your hack in the file
backend to use it if we're using a block device as backing file
works it's rather gross. Having the file backend general enough to
work with a block devices is fine, but adding special hacks that
only work on block device while having a fully working bio based backed
is a bit gross. Btw, at least on XFS you can implement discard using
hole punch operations, although that can lead to quite bad fragmentation
in cases. Just as block-level discards can lead to quite bad
performance - I'd suggest to not enable them by default.
One other thing I noticed is that you use igrab a lot. In general
drivers have absolutely no need for a igrab. If you have a reference
to the file behind an inode you keep the inode in core and there's no
need at all to grab a second reference to it.
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