logfs: create a pagecache page if it is not present

While writing the partial journal entries we assumed that the page
associated with the journal would always in locatable. This incorrect
assumption resulted in the following BUG

kernel BUG at /home/benixon/WD_SMR/kernels/linux-3.3.7-logfs/fs/logfs/journal.c:569!
EIP is at logfs_write_area+0xb6/0x109 [logfs]
EAX: 00000000 EBX: 00000000 ECX: ef6efea4 EDX: 00000000
ESI: 001b9000 EDI: f009e000 EBP: c3c13f14 ESP: c3c13ef0
DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Process sync (pid: 1799, ti=c3c12000 task=f07825b0 task.ti=c3c12000)
Stack:
01001000 c3c13f26 781b9000 00000000 f009e000 f7286000 f1f83400 f8445071
f1f83400 c3c13f30 f8445ae9 c3c13f20 0000100a 000ee000 f009e000 00000001
c3c13f5c f8445d17 c05eb0ee 00000000 f1f83400 ef718000 f009e25c ea9c3d80
Call Trace:
[<f8445071>] ? account_shadow+0x16d/0x16d [logfs]
[<f8445ae9>] logfs_write_je+0x2a/0x44 [logfs]
[<f8445d17>] logfs_write_anchor+0x114/0x228 [logfs]
[<c05eb0ee>] ? empty+0x5/0x5
[<f8444522>] logfs_sync_fs+0x1e/0x31 [logfs]
[<c051be66>] __sync_filesystem+0x5d/0x6f
[<c051be8d>] sync_one_sb+0x15/0x17
[<c04ff8b0>] iterate_supers+0x59/0x9a
[<c051be78>] ? __sync_filesystem+0x6f/0x6f
[<c051befc>] sys_sync+0x29/0x4f
[<c084285f>] sysenter_do_call+0x12/0x28
EIP: [<f8445127>] logfs_write_area+0xb6/0x109 [logfs] SS:ESP 0068:c3c13ef0
---[ end trace ef6e9ef52601a945 ]---

The fix is to create the pagecache page if it is not locatable.

Reported-and-tested-by: Benixon Dhas <Benixon.Dhas@wdc.com>
Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>
logfs: maintain the ordering of meta-inode destruction

LogFS does not use a specialized area to maintain the inodes. The
inodes information is kept in a specialized file called inode file.
Similarly, the segment information is kept in a segment file. Since
the segment file also has an inode which is kept in the inode file,
the inode for segment file must be evicted before the inode for inode
file. The change fixes the following BUG during unmount

Pid: 2057, comm: umount Not tainted 3.5.0-rc6+ #25 Bochs Bochs
RIP: 0010:[<ffffffffa005c5f2>]  [<ffffffffa005c5f2>] move_page_to_btree+0x32/0x1f0 [logfs]
Process umount (pid: 2057, threadinfo ...)
Call Trace:
[<ffffffff8112adca>] ? find_get_pages+0x2a/0x180
[<ffffffffa00549f5>] logfs_invalidatepage+0x85/0x90 [logfs]
[<ffffffff81136c51>] truncate_inode_page+0xb1/0xd0
[<ffffffff81136dcf>] truncate_inode_pages_range+0x15f/0x490
[<ffffffff81558549>] ? printk+0x78/0x7a
[<ffffffff81137185>] truncate_inode_pages+0x15/0x20
[<ffffffffa005b7fc>] logfs_evict_inode+0x6c/0x190 [logfs]
[<ffffffff8155c75b>] ? _raw_spin_unlock+0x2b/0x40
[<ffffffff8119e3d7>] evict+0xa7/0x1b0
[<ffffffff8119ea6e>] dispose_list+0x3e/0x60
[<ffffffff8119f1c4>] evict_inodes+0xf4/0x110
[<ffffffff81185b53>] generic_shutdown_super+0x53/0xf0
[<ffffffffa005d8f2>] logfs_kill_sb+0x52/0xf0 [logfs]
[<ffffffff81185ec5>] deactivate_locked_super+0x45/0x80
[<ffffffff81186a4a>] deactivate_super+0x4a/0x70
[<ffffffff811a228e>] mntput_no_expire+0xde/0x140
[<ffffffff811a30ff>] sys_umount+0x6f/0x3a0
[<ffffffff8155d8e9>] system_call_fastpath+0x16/0x1b
---[ end trace 45f7752082cefafd ]---

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