[Gluster-devel] zerofill() FOP

[Anand Avati]

It would be nice to make the fop match the writesame() semantics (@buf,
@len, @offset, @repeat) and just use it for zerofill as a specific use
case, by providing a 1 byte buffer storing a 0, repeated @len times.
Thoughts?

In the storage/bd layer, you can detect if the arguments are trying to
zero-fill (by inspecting @buf) and conditionally call ioctl(BLKZEROOUT).
This will prepare gluster for providing a more generic block layer
interface (in the furtue, for iSCSI?)

Avati

On Sun, Jun 9, 2013 at 8:53 PM, Bharata B Rao <bharata.rao at gmail.com> wrote:

> Hi,
>
> We are planning to add a new FOP to GlusterFS to exploit the WRITE
> SAME capability of the underlying block device in case of BD xlator.
> Linux has recently added support for WRITE SAME by means of a new
> ioctl (BLKZEROOUT) that can be used to zero-out a range of blocks. We
> are proposing the following FOP to support BLKZEROOUT ioctl in
> GlusterFS:
>
> int zerofill(struct glfs_fd *glfd, off_t offset, size_t len)
>
> This will zero-out the range of the file represented by @glfd,
> starting from @offset for @len bytes.
>
> Posix backend can implement the zerofill() in whatever way that is
> convenient/efficient, all it has do is to write zeroes to the file in
> the specified range.
>
> BD backend will issue ioctl(fd, BLKZEROOUT, params[2]) in response to
> zerofill(glfd, offset, len). param[0] is the starting sector number
> which should be derived from offset. param[1] is the nr_sectors which
> should be derived from len.
>
> Regards,
> Bharata.
> --
> http://raobharata.wordpress.com/
>
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