btrfs: only require sector size alignment for page read

If we're reading partial page, btrfs will warn about this as read/write
is always done in sector size, which now equals page size.

But for the upcoming subpage read-only support, our data read is only
aligned to sectorsize, which can be smaller than page size.

Thus here we change the warning condition to check it against
sectorsize, the behavior is not changed for regular sectorsize ==
PAGE_SIZE case, and won't report error for subpage read.

Also, pass the proper start/end with bv_offset for check_data_csum() to
handle.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -2823,6 +2823,7 @@ static void end_bio_extent_readpage(struct bio *bio)
 		struct page *page = bvec->bv_page;
 		struct inode *inode = page->mapping->host;
 		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+		u32 sectorsize = fs_info->sectorsize;
 
 		btrfs_debug(fs_info,
 			"end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
@@ -2831,24 +2832,25 @@ static void end_bio_extent_readpage(struct bio *bio)
 		tree = &BTRFS_I(inode)->io_tree;
 		failure_tree = &BTRFS_I(inode)->io_failure_tree;
 
-		/* We always issue full-page reads, but if some block
-		 * in a page fails to read, blk_update_request() will
-		 * advance bv_offset and adjust bv_len to compensate.
-		 * Print a warning for nonzero offsets, and an error
-		 * if they don't add up to a full page.  */
-		if (bvec->bv_offset || bvec->bv_len != PAGE_SIZE) {
-			if (bvec->bv_offset + bvec->bv_len != PAGE_SIZE)
-				btrfs_err(fs_info,
-					"partial page read in btrfs with offset %u and length %u",
-					bvec->bv_offset, bvec->bv_len);
-			else
-				btrfs_info(fs_info,
-					"incomplete page read in btrfs with offset %u and length %u",
-					bvec->bv_offset, bvec->bv_len);
-		}
-
-		start = page_offset(page);
-		end = start + bvec->bv_offset + bvec->bv_len - 1;
+		/*
+		 * We always issue full-sector reads, but if some block in a
+		 * page fails to read, blk_update_request() will advance
+		 * bv_offset and adjust bv_len to compensate.  Print a warning
+		 * for unaligned offsets, and an error if they don't add up to
+		 * a full sector.
+		 */
+		if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
+			btrfs_err(fs_info,
+		"partial page read in btrfs with offset %u and length %u",
+				  bvec->bv_offset, bvec->bv_len);
+		else if (!IS_ALIGNED(bvec->bv_offset + bvec->bv_len,
+				     sectorsize))
+			btrfs_info(fs_info,
+		"incomplete page read with offset %u and length %u",
+				   bvec->bv_offset, bvec->bv_len);
+
+		start = page_offset(page) + bvec->bv_offset;
+		end = start + bvec->bv_len - 1;
 		len = bvec->bv_len;
 
 		mirror = io_bio->mirror_num;