From b3d304167929bc199e6789fd67ffea035e7fdbf1 Mon Sep 17 00:00:00 2001
From: Jeremie Koenig <jk@jk.fr.eu.org>
Date: Mon, 23 Aug 2010 20:43:16 +0000
Subject: Refresh nodes when they're read from the start.

This is necessary for top, for instance, which keeps some files open and
re-reads them regularly. As an extra bonus we can drop the refresh hack.

* procfs.c, procfs.h: Remove the refresh hack.
  (procfs_refresh): New function, invalidates the cached contents.
* netfs.c (netfs_attempt_read, netfs_get_dirents): Call
  procfs_refresh when the read is from offset 0.
* proclist.c (proclist_make_node): Remove the refresh hack.
* dircat.c (dircat_make_node): Likewise.
  (dircat_get_contents): Use procfs_refresh to avoid keeping old data
  from the component nodes.
---
 dircat.c   |  5 +++--
 netfs.c    |  6 ++++++
 procfs.c   | 19 +++++++++----------
 procfs.h   | 13 +++++--------
 proclist.c |  1 -
 5 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/dircat.c b/dircat.c
index d043486..d24e834 100644
--- a/dircat.c
+++ b/dircat.c
@@ -23,6 +23,9 @@ dircat_get_contents (void *hook, char **contents, ssize_t *contents_len)
       char *subcon;
       ssize_t sublen;
 
+      /* Make sure we're not getting some old stuff.  */
+      procfs_refresh (dcn->dirs[i]);
+
       err = procfs_get_contents (dcn->dirs[i], &subcon, &sublen);
       if (err)
         {
@@ -83,8 +86,6 @@ dircat_make_node (struct node *const *dirs, int num_dirs)
     .cleanup_contents = procfs_cleanup_contents_with_free,
     .lookup = dircat_lookup,
     .cleanup = dircat_cleanup,
-    /* necessary so that it propagates to proclist */
-    .enable_refresh_hack_and_break_readdir = 1,
   };
   struct dircat_node *dcn;
   int i;
diff --git a/netfs.c b/netfs.c
index e41e062..02a4bf5 100644
--- a/netfs.c
+++ b/netfs.c
@@ -57,6 +57,9 @@ error_t netfs_attempt_read (struct iouser *cred, struct node *np,
   ssize_t contents_len;
   error_t err;
 
+  if (offset == 0)
+    procfs_refresh (np);
+
   err = procfs_get_contents (np, &contents, &contents_len);
   if (err)
     return err;
@@ -139,6 +142,9 @@ error_t netfs_get_dirents (struct iouser *cred, struct node *dir,
   char *contents;
   ssize_t contents_len;
   error_t err;
+
+  if (entry == 0)
+    procfs_refresh (dir);
  
   err = procfs_get_contents (dir, &contents, &contents_len);
   if (err)
diff --git a/procfs.c b/procfs.c
index 6d15e4f..f7b2834 100644
--- a/procfs.c
+++ b/procfs.c
@@ -111,14 +111,6 @@ procfs_make_ino (struct node *np, const char *filename)
 
 error_t procfs_get_contents (struct node *np, char **data, ssize_t *data_len)
 {
-  if (np->nn->ops->enable_refresh_hack_and_break_readdir && np->nn->contents)
-    {
-      if (np->nn->ops->cleanup_contents)
-	np->nn->ops->cleanup_contents (np->nn->hook, np->nn->contents,
-				       np->nn->contents_len);
-      np->nn->contents = NULL;
-    }
-
   if (! np->nn->contents && np->nn->ops->get_contents)
     {
       char *contents;
@@ -141,6 +133,14 @@ error_t procfs_get_contents (struct node *np, char **data, ssize_t *data_len)
   return 0;
 }
 
+void procfs_refresh (struct node *np)
+{
+  if (np->nn->contents && np->nn->ops->cleanup_contents)
+    np->nn->ops->cleanup_contents (np->nn->hook, np->nn->contents, np->nn->contents_len);
+
+  np->nn->contents = NULL;
+}
+
 error_t procfs_lookup (struct node *np, const char *name, struct node **npp)
 {
   error_t err = ENOENT;
@@ -172,8 +172,7 @@ error_t procfs_lookup (struct node *np, const char *name, struct node **npp)
 
 void procfs_cleanup (struct node *np)
 {
-  if (np->nn->contents && np->nn->ops->cleanup_contents)
-    np->nn->ops->cleanup_contents (np->nn->hook, np->nn->contents, np->nn->contents_len);
+  procfs_refresh (np);
 
   if (np->nn->ops->cleanup)
     np->nn->ops->cleanup (np->nn->hook);
diff --git a/procfs.h b/procfs.h
index e8ef18b..a9665f9 100644
--- a/procfs.h
+++ b/procfs.h
@@ -32,14 +32,6 @@ struct procfs_node_ops
 
   /* Destroy this node.  */
   void (*cleanup) (void *hook);
-
-  /* FIXME: This is needed because the root node is persistent, and we
-     want the list of processes to be updated. However, this means that
-     readdir() on the root node runs the risk of returning incoherent
-     results if done in multiple runs and processes are added/removed in
-     the meantime.  The right way to fix this is probably to add a
-     getroot() user hook function to libnetfs.  */
-  int enable_refresh_hack_and_break_readdir;
 };
 
 /* These helper functions can be used as procfs_node_ops.cleanup_contents. */
@@ -71,6 +63,11 @@ void procfs_node_chtype (struct node *np, mode_t type);
    corresponding child nodes.  */
 ino64_t procfs_make_ino (struct node *np, const char *filename);
 
+/* Forget the current cached contents for the node.  This is done before reads
+   from offset 0, to ensure that the data are recent even for utilities such as
+   top which keep some nodes open.  */
+void procfs_refresh (struct node *np);
+
 error_t procfs_get_contents (struct node *np, char **data, ssize_t *data_len);
 error_t procfs_lookup (struct node *np, const char *name, struct node **npp);
 void procfs_cleanup (struct node *np);
diff --git a/proclist.c b/proclist.c
index 38368fe..fe5d0cf 100644
--- a/proclist.c
+++ b/proclist.c
@@ -69,7 +69,6 @@ proclist_make_node (struct ps_context *pc)
     .get_contents = proclist_get_contents,
     .lookup = proclist_lookup,
     .cleanup_contents = procfs_cleanup_contents_with_free,
-    .enable_refresh_hack_and_break_readdir = 1,
   };
   return procfs_make_node (&ops, pc);
 }
-- 
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