[RFC 2/6] fs: introduce count_open_files()

[Tycho Andersen <tycho@tycho.pizza>]

From: Tycho Andersen <tandersen@netflix.com>

In future patches, we'll need a count of the number of open file
descriptors for misc NOFILE cgroup migration, so introduce a helper to do
this.

Signed-off-by: Tycho Andersen <tandersen@netflix.com>
---
 fs/file.c               | 10 ++++++++++
 include/linux/fdtable.h |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/fs/file.c b/fs/file.c
index b1633c00bd3c..539bead2364e 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -285,6 +285,16 @@ static unsigned int count_possible_open_files(struct fdtable *fdt)
 	return i;
 }
 
+u64 count_open_files(struct fdtable *fdt)
+{
+	int i;
+	u64 retval = 0;
+
+	for (i = 0; i < DIV_ROUND_UP(fdt->max_fds, BITS_PER_LONG); i++)
+		retval += hweight64((__u64)fdt->open_fds[i]);
+	return retval;
+}
+
 /*
  * Note that a sane fdtable size always has to be a multiple of
  * BITS_PER_LONG, since we have bitmaps that are sized by this.
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index bc4c3287a65e..d74234c5d4e9 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -77,6 +77,8 @@ struct dentry;
 #define files_fdtable(files) \
 	rcu_dereference_check_fdtable((files), (files)->fdt)
 
+u64 count_open_files(struct fdtable *fdt);
+
 /*
  * The caller must ensure that fd table isn't shared or hold rcu or file lock
  */
-- 
2.34.1