[PATCH v3] btrfs-progs: property: introduce drop_subtree_threshold property

[Sidong Yang <realwakka@gmail.com>]

This patch introduces new property drop_subtree_threshold. This property
could be set/get easily by root dir without find sysfs path.

Fixes: https://github.com/kdave/btrfs-progs/issues/795

Issue: #795
Signed-off-by: Sidong Yang <realwakka@gmail.com>
---
v2: error msg for -ENOENT, fix desc for prop
v3: warn msg and return 0 for -ENOENT, fix style
---
 cmds/property.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/cmds/property.c b/cmds/property.c
index a36b5ab2..42c372dd 100644
--- a/cmds/property.c
+++ b/cmds/property.c
@@ -35,6 +35,7 @@
 #include "common/utils.h"
 #include "common/help.h"
 #include "common/filesystem-utils.h"
+#include "common/sysfs-utils.h"
 #include "cmds/commands.h"
 #include "cmds/props.h"
 
@@ -236,6 +237,49 @@ out:
 
 	return ret;
 }
+static int prop_drop_subtree_threshold(enum prop_object_type type,
+				       const char *object,
+				       const char *name,
+				       const char *value,
+				       bool force)
+{
+	int ret;
+	int fd;
+	int sysfs_fd;
+	char buf[255];
+
+	fd = btrfs_open_path(object, value, false);
+	if (fd < 0)
+		return -errno;
+
+	sysfs_fd = sysfs_open_fsid_file(fd, "qgroups/drop_subtree_threshold");
+	if (sysfs_fd < 0) {
+		ret = sysfs_fd;
+		if (ret == -ENOENT) {
+			warning("failed to access qgroups/drop_subtree_threshold for %s, quota should be enabled for this property: %m",
+				object);
+			ret = 0;
+		}
+		close(fd);
+		return ret;
+	}
+
+	if (value) {
+		ret = write(sysfs_fd, value, strlen(value));
+	} else {
+		ret = read(sysfs_fd, buf, 255);
+		if (ret > 0) {
+			buf[ret] = 0;
+			pr_verbose(LOG_DEFAULT, "drop_subtree_threshold=%s", buf);
+		}
+	}
+
+	ret = ret < 0 ? -errno : 0;
+
+	close(sysfs_fd);
+	close(fd);
+	return ret;
+}
 
 const struct prop_handler prop_handlers[] = {
 	{
@@ -259,6 +303,13 @@ const struct prop_handler prop_handlers[] = {
 		.types = prop_object_inode,
 		.handler = prop_compression
 	},
+	{
+		.name = "drop_subtree_threshold",
+		.desc = "subtree level threshold to mark qgroup inconsistent during snapshot deletion, can reduce qgroup workload of snapshot deletion",
+		.read_only = 0,
+		.types = prop_object_root,
+		.handler = prop_drop_subtree_threshold
+	},
 	{NULL, NULL, 0, 0, NULL}
 };
 
-- 
2.43.0