btrfs-progs: tune: properly open zoned devices for RW

[BUG]
There is a report that, for zoned devices btrfstune is unable to convert
it to block group tree.

 # btrfstune /dev/nullb0 --convert-to-block-group-tree
 Error reading 1342193664, -1
 Error reading 1342193664, -1
 ERROR: cannot read chunk root
 ERROR: open ctree failed

[CAUSE]
For read-write opened zoned devices, all the read/write has to be
aligned to its sector size.

However btrfs stores its metadata by extent_buffer::data[], which has
all the structures before it, thus never aligned to zoned device sector
size.

Normally we would require btrfs_pread() and btrfs_pwrite() to do the
extra alignment, but during open_ctree(), we are not aware if a device
is zoned or not.

Thus we rely on if the fd is opened with O_DIRECT flag, if the fd has
O_DIRECT, then we would temporarily set fs_info->zoned for chunk tree
read.

Unforunately not all open_ctree_fd() callers have the flags set
properly, and btrfstune is one of the missing call site.

This makes all the read not properly aligned and cause read failure.

[FIX]
Just manually check if the target device is a zoned one, and set
O_DIRECT accordingly.

Issue: #765
Reviewed-by: Johannes Thumshirn <[email protected]>
Reviewed-by: Naohiro Aota <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Signed-off-by: David Sterba <[email protected]>

tune/main.c

@@ -29,6 +29,7 @@
 #include "kernel-shared/transaction.h"
 #include "kernel-shared/volumes.h"
 #include "kernel-shared/free-space-tree.h"
+#include "kernel-shared/zoned.h"
 #include "common/utils.h"
 #include "common/open-utils.h"
 #include "common/device-scan.h"
@@ -193,6 +194,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
 	u64 super_flags = 0;
 	int quota = 0;
 	int fd = -1;
+	int oflags = O_RDWR;
 
 	btrfs_config_init();
 
@@ -336,7 +338,9 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
 		}
 	}
 
-	fd = open(device, O_RDWR);
+	if (zoned_model(device) == ZONED_HOST_MANAGED)
+		oflags |= O_DIRECT;
+	fd = open(device, oflags);
 	if (fd < 0) {
 		error("mount check: cannot open %s: %m", device);
 		ret = 1;