[PATCH 2/4] btrfs-progs: check read extent errors when mapping

[Zach Brown <zab@zabbo.net>]

coverity barked out a warning that btrfs-map-logical was storing but
ignoring errors from read_extent_from_disk().   So don't ignore 'em.  I
made extent reading errors fatal to match the fatal errors from mapping
mirrors above.

And while we're at it have read_extent_from_disk() return -errno pread
errors instead of -EIO or -1 (-EPERM).  The only other caller who tests
errors clobbers them with -EIO.

Signed-off-by: Zach Brown <zab@zabbo.net>
---
 btrfs-map-logical.c | 12 +++++++++++-
 extent_io.c         |  4 +++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/btrfs-map-logical.c b/btrfs-map-logical.c
index 6b475fc..47d1104 100644
--- a/btrfs-map-logical.c
+++ b/btrfs-map-logical.c
@@ -76,8 +76,18 @@ static struct extent_buffer * debug_read_block(struct btrfs_root *root,
 			(unsigned long long)eb->dev_bytenr, device->name);
 		kfree(multi);
 
-		if (!copy || mirror_num == copy)
+		if (!copy || mirror_num == copy) {
 			ret = read_extent_from_disk(eb, 0, eb->len);
+			if (ret) {
+				fprintf(info_file,
+					"Error: failed to read extent: mirror %d logical %llu: %s\n",
+					mirror_num, (unsigned long long)eb->start,
+					strerror(-ret));
+				free_extent_buffer(eb);
+				eb = NULL;
+				break;
+			}
+		}
 
 		num_copies = btrfs_num_copies(&root->fs_info->mapping_tree,
 					      eb->start, eb->len);
diff --git a/extent_io.c b/extent_io.c
index 425af8a..5186e89 100644
--- a/extent_io.c
+++ b/extent_io.c
@@ -647,8 +647,10 @@ int read_extent_from_disk(struct extent_buffer *eb,
 {
 	int ret;
 	ret = pread(eb->fd, eb->data + offset, len, eb->dev_bytenr);
-	if (ret < 0)
+	if (ret < 0) {
+		ret = -errno;
 		goto out;
+	}
 	if (ret != len) {
 		ret = -EIO;
 		goto out;
-- 
1.9.3