[PATCH 5.10 693/770] NFSD: Flesh out a documenting comment for filecache.c

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5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

[ Upstream commit b3276c1f5b268ff56622e9e125b792b4c3dc03ac ]

Record what we've learned recently about the NFSD filecache in a
documenting comment so our future selves don't forget what all this
is for.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/nfsd/filecache.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 13a25503b80e1..d681faf48cf85 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -2,6 +2,30 @@
  * Open file cache.
  *
  * (c) 2015 - Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
+ *
+ * An nfsd_file object is a per-file collection of open state that binds
+ * together:
+ *   - a struct file *
+ *   - a user credential
+ *   - a network namespace
+ *   - a read-ahead context
+ *   - monitoring for writeback errors
+ *
+ * nfsd_file objects are reference-counted. Consumers acquire a new
+ * object via the nfsd_file_acquire API. They manage their interest in
+ * the acquired object, and hence the object's reference count, via
+ * nfsd_file_get and nfsd_file_put. There are two varieties of nfsd_file
+ * object:
+ *
+ *  * non-garbage-collected: When a consumer wants to precisely control
+ *    the lifetime of a file's open state, it acquires a non-garbage-
+ *    collected nfsd_file. The final nfsd_file_put releases the open
+ *    state immediately.
+ *
+ *  * garbage-collected: When a consumer does not control the lifetime
+ *    of open state, it acquires a garbage-collected nfsd_file. The
+ *    final nfsd_file_put allows the open state to linger for a period
+ *    during which it may be re-used.
  */
 
 #include <linux/hash.h>
-- 
2.43.0







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