[PATCH] 9p: document short read behaviour with O_NONBLOCK

[Dominique Martinet <asmadeus@codewreck.org>]

From: Dominique Martinet <dominique.martinet@cea.fr>

Regular files opened with O_NONBLOCK allow read to return after a single
round-trip with the server instead of trying to fill buffer.
Add a few lines in 9p documentation to describe that.

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---
 Documentation/filesystems/9p.txt | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/filesystems/9p.txt b/Documentation/filesystems/9p.txt
index fec7144e817c..3fb780ffdf23 100644
--- a/Documentation/filesystems/9p.txt
+++ b/Documentation/filesystems/9p.txt
@@ -133,6 +133,16 @@ OPTIONS
 		cache tags for existing cache sessions can be listed at
 		/sys/fs/9p/caches. (applies only to cache=fscache)
 
+BEHAVIOR
+========
+
+This section aims at describing 9p 'quirks' that can be different
+from a local filesystem behaviors.
+
+ - Setting O_NONBLOCK on a file will make client reads return as early
+   as the server returns some data instead of trying to fill the read
+   buffer with the requested amount of bytes or end of file is reached.
+
 RESOURCES
 =========
 
-- 
2.26.0