From c66c6e0c0b04ce4a152fe02c562dd0752665d580 Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Thu, 1 Nov 2012 08:39:26 -0500 Subject: [PATCH] rbd: document rbd_spec structure I promised Josh I would document whether there were any restrictions needed for accessing fields of an rbd_spec structure. This adds a big block of comments that documents the structure and how it is used--including the fact that we don't attempt to synchronize access to it. Signed-off-by: Alex Elder Reviewed-by: David Zafman Reviewed-by: Josh Durgin --- drivers/block/rbd.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 89576a0b3f2e..128978c6a4e0 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -119,7 +119,26 @@ struct rbd_image_header { * An rbd image specification. * * The tuple (pool_id, image_id, snap_id) is sufficient to uniquely - * identify an image. + * identify an image. Each rbd_dev structure includes a pointer to + * an rbd_spec structure that encapsulates this identity. + * + * Each of the id's in an rbd_spec has an associated name. For a + * user-mapped image, the names are supplied and the id's associated + * with them are looked up. For a layered image, a parent image is + * defined by the tuple, and the names are looked up. + * + * An rbd_dev structure contains a parent_spec pointer which is + * non-null if the image it represents is a child in a layered + * image. This pointer will refer to the rbd_spec structure used + * by the parent rbd_dev for its own identity (i.e., the structure + * is shared between the parent and child). + * + * Since these structures are populated once, during the discovery + * phase of image construction, they are effectively immutable so + * we make no effort to synchronize access to them. + * + * Note that code herein does not assume the image name is known (it + * could be a null pointer). */ struct rbd_spec { u64 pool_id; -- 2.39.5