squashfs: migrate from ll_rw_block usage to BIO

ll_rw_block() function has been deprecated in favor of BIO which appears
to come with large performance improvements.

This patch decreases boot time by close to 40% when using squashfs for
the root file-system.  This is observed at least in the context of
starting an Android VM on Chrome OS using crosvm.  The patch was tested
on 4.19 as well as master.

This patch is largely based on Adrien Schildknecht's patch that was
originally sent as https://lkml.org/lkml/2017/9/22/814 though with some
significant changes and simplifications while also taking Phillip
Lougher's feedback into account, around preserving support for
FILE_CACHE in particular.

[akpm@linux-foundation.org: fix build error reported by Randy]
  Link: http://lkml.kernel.org/r/319997c2-5fc8-f889-2ea3-d913308a7c1f@infradead.org
Signed-off-by: Philippe Liard <pliard@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Adrien Schildknecht <adrien+dev@schischi.me>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Daniel Rosenberg <drosen@google.com>
Link: https://chromium.googlesource.com/chromiumos/platform/crosvm
Link: http://lkml.kernel.org/r/20191106074238.186023-1-pliard@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 29 insertions, 22 deletions

diff --git a/fs/squashfs/xz_wrapper.c b/fs/squashfs/xz_wrapper.c
index 4b2f2051a6dc..e80419aed862 100644
--- a/fs/squashfs/xz_wrapper.c
+++ b/fs/squashfs/xz_wrapper.c
@@ -10,7 +10,7 @@
 
 
 #include <linux/mutex.h>
-#include <linux/buffer_head.h>
+#include <linux/bio.h>
 #include <linux/slab.h>
 #include <linux/xz.h>
 #include <linux/bitops.h>
@@ -117,11 +117,12 @@ static void squashfs_xz_free(void *strm)
 
 
 static int squashfs_xz_uncompress(struct squashfs_sb_info *msblk, void *strm,
-	struct buffer_head **bh, int b, int offset, int length,
+	struct bio *bio, int offset, int length,
 	struct squashfs_page_actor *output)
 {
-	enum xz_ret xz_err;
-	int avail, total = 0, k = 0;
+	struct bvec_iter_all iter_all = {};
+	struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
+	int total = 0, error = 0;
 	struct squashfs_xz *stream = strm;
 
 	xz_dec_reset(stream->state);
@@ -131,11 +132,23 @@ static int squashfs_xz_uncompress(struct squashfs_sb_info *msblk, void *strm,
 	stream->buf.out_size = PAGE_SIZE;
 	stream->buf.out = squashfs_first_page(output);
 
-	do {
-		if (stream->buf.in_pos == stream->buf.in_size && k < b) {
-			avail = min(length, msblk->devblksize - offset);
+	for (;;) {
+		enum xz_ret xz_err;
+
+		if (stream->buf.in_pos == stream->buf.in_size) {
+			const void *data;
+			int avail;
+
+			if (!bio_next_segment(bio, &iter_all)) {
+				/* XZ_STREAM_END must be reached. */
+				error = -EIO;
+				break;
+			}
+
+			avail = min(length, ((int)bvec->bv_len) - offset);
+			data = page_address(bvec->bv_page) + bvec->bv_offset;
 			length -= avail;
-			stream->buf.in = bh[k]->b_data + offset;
+			stream->buf.in = data + offset;
 			stream->buf.in_size = avail;
 			stream->buf.in_pos = 0;
 			offset = 0;
@@ -150,23 +163,17 @@ static int squashfs_xz_uncompress(struct squashfs_sb_info *msblk, void *strm,
 		}
 
 		xz_err = xz_dec_run(stream->state, &stream->buf);
-
-		if (stream->buf.in_pos == stream->buf.in_size && k < b)
-			put_bh(bh[k++]);
-	} while (xz_err == XZ_OK);
+		if (xz_err == XZ_STREAM_END)
+			break;
+		if (xz_err != XZ_OK) {
+			error = -EIO;
+			break;
+		}
+	}
 
 	squashfs_finish_page(output);
 
-	if (xz_err != XZ_STREAM_END || k < b)
-		goto out;
-
-	return total + stream->buf.out_pos;
-
-out:
-	for (; k < b; k++)
-		put_bh(bh[k]);
-
-	return -EIO;
+	return error ? error : total + stream->buf.out_pos;
 }
 
 const struct squashfs_decompressor squashfs_xz_comp_ops = {