[PATCH 6/6 v2] Btrfs: add send_stream_version attribute to sysfs

[Filipe David Borba Manana]

So that applications can find out what's the highest send stream
version supported/implemented by the running kernel:

    $ cat /sys/fs/btrfs/send/stream_version
    2

Signed-off-by: Filipe David Borba Manana <fdman...@gmail.com>
---

V2: Renamed /sys/fs/btrfs/send_stream_version to 
/sys/fs/btrfs/send/stream_version,
    as in the future it might be useful to add other sysfs attrbutes related to
    send (other ro information or tunables like internal buffer sizes, etc).

 fs/btrfs/send.h  |  1 +
 fs/btrfs/sysfs.c | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/fs/btrfs/send.h b/fs/btrfs/send.h
index 987936c..047fd6d 100644
--- a/fs/btrfs/send.h
+++ b/fs/btrfs/send.h
@@ -22,6 +22,7 @@
 #define BTRFS_SEND_STREAM_MAGIC "btrfs-stream"
 #define BTRFS_SEND_STREAM_VERSION_1 1
 #define BTRFS_SEND_STREAM_VERSION_2 2
+#define BTRFS_SEND_STREAM_VERSION_LATEST BTRFS_SEND_STREAM_VERSION_2
 
 #define BTRFS_SEND_BUF_SIZE (1024 * 64)
 #define BTRFS_SEND_READ_SIZE (1024 * 48)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 58a1dd1..d93c0b5 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -31,6 +31,7 @@
 #include "transaction.h"
 #include "sysfs.h"
 #include "volumes.h"
+#include "send.h"
 
 static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj);
 
@@ -662,6 +663,26 @@ static int btrfs_init_debugfs(void)
        return 0;
 }
 
+static ssize_t send_stream_version_show(struct kobject *kobj,
+                                       struct kobj_attribute *a,
+                                       char *buf)
+{
+       return snprintf(buf, PAGE_SIZE, "%d\n",
+                       BTRFS_SEND_STREAM_VERSION_LATEST);
+}
+
+BTRFS_ATTR(stream_version, 0444, send_stream_version_show);
+
+static struct attribute *btrfs_send_attrs[] = {
+       BTRFS_ATTR_PTR(stream_version),
+       NULL
+};
+
+static const struct attribute_group btrfs_send_attr_group = {
+       .name = "send",
+       .attrs = btrfs_send_attrs,
+};
+
 int btrfs_init_sysfs(void)
 {
        int ret;
@@ -678,8 +699,13 @@ int btrfs_init_sysfs(void)
        ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
        if (ret)
                goto out2;
+       ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_send_attr_group);
+       if (ret)
+               goto out3;
 
        return 0;
+out3:
+       sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
 out2:
        debugfs_remove_recursive(btrfs_debugfs_root_dentry);
 out1:
@@ -691,6 +717,7 @@ out1:
 void btrfs_exit_sysfs(void)
 {
        sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
+       sysfs_remove_group(&btrfs_kset->kobj, &btrfs_send_attr_group);
        kset_unregister(btrfs_kset);
        debugfs_remove_recursive(btrfs_debugfs_root_dentry);
 }
-- 
1.9.1

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