From 48180e15d3eaff51b1da30a90bc64b7acba8fb51 Mon Sep 17 00:00:00 2001
From: Marek Behún
Date: Mon, 30 Mar 2020 18:48:42 +0200
Subject: fs: btrfs: support sparse extents

When logical address of a regular extent is 0, the extent is sparse and
consists of all zeros.

Without this when sparse extents are used in a file reading fails with
  Cannot map logical address 0 to physical

Signed-off-by: Marek Behún <marek.behun@nic.cz>
---
 fs/btrfs/extent-io.c | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'fs')

diff --git a/fs/btrfs/extent-io.c b/fs/btrfs/extent-io.c
index 66d0e1c7d65..2e4599cf64a 100644
--- a/fs/btrfs/extent-io.c
+++ b/fs/btrfs/extent-io.c
@@ -78,6 +78,12 @@ u64 btrfs_read_extent_reg(struct btrfs_path *path,
 	if (size > dlen - offset)
 		size = dlen - offset;
 
+	/* sparse extent */
+	if (extent->disk_bytenr == 0) {
+		memset(out, 0, size);
+		return size;
+	}
+
 	physical = btrfs_map_logical_to_physical(extent->disk_bytenr);
 	if (physical == -1ULL)
 		return -1ULL;
-- 
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