From: Prasad Joshi <prasadjoshi.linux@gmail.com>
Date: Mon, 23 Jul 2012 05:02:11 +0000 (+0530)
Subject: logfs: query block device for number of pages to send with bio
X-Git-Tag: v3.6-rc4~10^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f0bbd8ca7905fcc0602c038013b095322fec939;p=pandora-kernel.git

logfs: query block device for number of pages to send with bio

The block device driver puts a limit on maximum number of pages that
can be sent with the bio. Not all block devices can handle
BIO_MAX_PAGES number of pages in bio. Specifically the virtio-blk
diriver limits it to 126. When the LogFS file system was excersized in
KVM, the following bug from do_virtblk_request() was observed

static void do_virtblk_request(struct request_queue *q)
{
	....
	....
	while ((req = blk_peek_request(q)) != NULL) {
		BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
		....
		....
	}
	....
}

The patch fixes the problem by querring the maximum number of pages in
bio allowed from block device driver and then using those many pages
during submit_bio.

Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>
---

Reading git-diff-tree failed