X-Git-Url: http://git.tuebingen.mpg.de/?a=blobdiff_plain;f=Filesystems.m4;h=ca894346e55d865ee7171c1052c22a01a005acf4;hb=63ef3ef23517d1f63b4a17da8cecb88b8fa1ebdf;hp=9035de5218f1ab8da1e4c6e399438f2b523002a8;hpb=d9515637ca709f2ad9fbb4e1e90690981b8db1ad;p=aple.git

diff --git a/Filesystems.m4 b/Filesystems.m4
index 9035de5..ca89434 100644
--- a/Filesystems.m4
+++ b/Filesystems.m4
@@ -955,6 +955,11 @@ file fragmentation, but they can cause confusion because they are
 accounted identically to other blocks, making files appear to use
 more data blocks than expected. </p>
 
+<p> If the system crashes while preallocated post-EOF blocks exist,
+the space will be recovered the next time the affected file gets closed
+(after it has been opened of course) by the normal reclaim mechanism
+which happens when a file is being closed. </p>
+
 SUBSECTION(«Reverse Mapping»)
 
 <p> This feature was implemented in 2018. It adds yet another B-tree to
@@ -1199,7 +1204,7 @@ re-used subsequently. File handles are based on <em>leases</em>:
 The client periodically talks to the server to update its leases. </p>
 
 <p> There is a deep interaction between file handles and the dentry
-cache of the vfs. Without nfs, a filesystems can rely on the following
+cache of the vfs. Without nfs, a filesystem can rely on the following
 "closure" property: For any positive dentry, all its parent directories
 are also positive dentries. This is no longer true if a filesystem
 is exported. Therefore the filesystem maps any file handles sent to
@@ -1340,11 +1345,16 @@ is still open. Only after all the last file descriptor that refers
 to the thusly silly-renamed file is closed, the client removes the
 file by issuing an appropriate rpc. </p>
 
-<p> This approach is not perfect. For one, if the client crashes,
-a stale <code>.nfs12345</code> file remains on the server. Second,
-since silly renames are only known to the nfs client, bad things
-happen if a different client removes the file. </p>
-
+<p> This approach is not perfect. For one, if the client crashes, a
+stale <code>.nfs12345</code> file remains on the server. Second, since
+silly renames are only known to the nfs client, bad things happen if a
+different client removes the file. Finally, if an application running
+on a client removes the last regular file in a directory, and this
+file got silly-renamed because it was still held open, a subsequent
+<code>rmdir</code> will fail unexpectedly with <code>Directory not
+empty</code>. Version 4.1 of the NFS protocol finally got rid of
+silly renames: An NFS4.1 server knows when it its safe to unlink a
+file and communicates this information to the client. </p>
 
 <p> The file handle which an nfs client received through some earlier
 rpc can become invalid at any time due to operations on a different
@@ -1391,11 +1401,11 @@ EXERCISES()
 	<li> On an nfs server, run <code>collectl -s F -i 5</code> and discuss
 	the output. </li>
 
-	<li> In an nfs-mounted directory, run <code>cat > foo &</code>. Note
-	that the cat process automatically receives the STOP signal.
-	Run <code>rm foo; ls -ltra</code>. Read section D2 of the
-	<a href="http://nfs.sourceforge.net/">nfs HOWTO</a> for the
-	explanation. </li>
+	<li> In an nfs-mounted directory (nfs version 4.0 or earlier), run
+	<code>cat > foo &</code>. Note that the cat process automatically
+	receives the STOP signal. Run <code>rm foo; ls -ltra</code>. Read
+	section D2 of the <a href="http://nfs.sourceforge.net/">nfs HOWTO</a>
+	for the explanation. </li>
 
 	<li> In an nfs-mounted directory, run <code>{ while :; do echo; sleep
 	1; done; } > baz &</code>. What happens if you remove the file on a