[RFC PATCH] ceph: add remote object copy counter to fs client

["Luís Henriques" <lhenriques@suse.de>]

This counter will keep track of the number of remote object copies done on
copy_file_range syscalls.  This counter will be filesystem per-client, and
can be accessed from the client debugfs directory.

Cc: Patrick Donnelly <pdonnell@redhat.com>
Signed-off-by: Luís Henriques <lhenriques@suse.de>
---
This is an RFC to reply to Patrick's request in [0].  Note that I'm not
100% sure about the usefulness of this patch, or if this is the best way
to provide the functionality Patrick requested.  Anyway, this is just to
get some feedback, hence the RFC.

Cheers,
--
Luís

[0] https://github.com/ceph/ceph/pull/42720

 fs/ceph/debugfs.c | 17 ++++++++++++++++-
 fs/ceph/file.c    |  1 +
 fs/ceph/super.c   |  1 +
 fs/ceph/super.h   |  2 ++
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 38b78b45811f..09f4c04ade0e 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -346,13 +346,22 @@ static int status_show(struct seq_file *s, void *p)
 	return 0;
 }
 
+static int copyfrom_show(struct seq_file *s, void *p)
+{
+	struct ceph_fs_client *fsc = s->private;
+
+	seq_printf(s, "%llu\n", atomic64_read(&fsc->copyfrom_count));
+
+	return 0;
+}
+
 DEFINE_SHOW_ATTRIBUTE(mdsmap);
 DEFINE_SHOW_ATTRIBUTE(mdsc);
 DEFINE_SHOW_ATTRIBUTE(caps);
 DEFINE_SHOW_ATTRIBUTE(mds_sessions);
 DEFINE_SHOW_ATTRIBUTE(metric);
 DEFINE_SHOW_ATTRIBUTE(status);
-
+DEFINE_SHOW_ATTRIBUTE(copyfrom);
 
 /*
  * debugfs
@@ -387,6 +396,7 @@ void ceph_fs_debugfs_cleanup(struct ceph_fs_client *fsc)
 	debugfs_remove(fsc->debugfs_caps);
 	debugfs_remove(fsc->debugfs_metric);
 	debugfs_remove(fsc->debugfs_mdsc);
+	debugfs_remove(fsc->debugfs_copyfrom);
 }
 
 void ceph_fs_debugfs_init(struct ceph_fs_client *fsc)
@@ -443,6 +453,11 @@ void ceph_fs_debugfs_init(struct ceph_fs_client *fsc)
 						  fsc->client->debugfs_dir,
 						  fsc,
 						  &status_fops);
+	fsc->debugfs_copyfrom = debugfs_create_file("copyfrom",
+						    0400,
+						    fsc->client->debugfs_dir,
+						    fsc,
+						    &copyfrom_fops);
 }
 
 
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index d16fd2d5fd42..bbeb437ca4bf 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -2254,6 +2254,7 @@ static ssize_t ceph_do_objects_copy(struct ceph_inode_info *src_ci, u64 *src_off
 				bytes = ret;
 			goto out;
 		}
+		atomic64_inc(&fsc->copyfrom_count);
 		len -= object_size;
 		bytes += object_size;
 		*src_off += object_size;
diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 9b1b7f4cfdd4..4972554185e3 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -670,6 +670,7 @@ static struct ceph_fs_client *create_fs_client(struct ceph_mount_options *fsopt,
 	fsc->have_copy_from2 = true;
 
 	atomic_long_set(&fsc->writeback_count, 0);
+	atomic64_set(&fsc->copyfrom_count, 0);
 
 	err = -ENOMEM;
 	/*
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index a40eb14c282a..65846beca418 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -119,6 +119,7 @@ struct ceph_fs_client {
 	struct ceph_mds_client *mdsc;
 
 	atomic_long_t writeback_count;
+	atomic64_t copyfrom_count;
 
 	struct workqueue_struct *inode_wq;
 	struct workqueue_struct *cap_wq;
@@ -131,6 +132,7 @@ struct ceph_fs_client {
 	struct dentry *debugfs_metric;
 	struct dentry *debugfs_status;
 	struct dentry *debugfs_mds_sessions;
+	struct dentry *debugfs_copyfrom;
 #endif
 
 #ifdef CONFIG_CEPH_FSCACHE