patch-1.3.82 linux/fs/nfs/README

• Lines: 115
• Date: Sun Mar 31 20:27:59 1996
• Orig file: v1.3.81/linux/fs/nfs/README
• Orig date: Thu Jan 1 02:00:00 1970

diff -u --recursive --new-file v1.3.81/linux/fs/nfs/README linux/fs/nfs/README
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+
+
+    This is an NFS client for Linux that supports async RPC calls for
+    read-ahead (and hopefully soon, write-back) on regular files. 
+
+    The implementation uses a straightforward nfsiod scheme.  After
+    trying out a number of different concepts, I finally got back to
+    this concept, because everything else either didn't work or gave me
+    headaches. It's not flashy, but it works without hacking into any
+    other regions of the kernel.
+
+
+    HOW TO USE
+
+    This stuff compiles as a loadable module (I developed it on 1.3.77).
+    Simply type mkmodule, and insmod nfs.o. This will start for nfsiod's
+    at the same time (which will show up under the pesudonym of insmod in
+    ps-style listings).
+
+    Alternatively, you can put it right into the kernel: remove everything
+    from fs/nfs, move the Makefile and all *.c to this directory, and
+    copy all *.h files to include/linux.
+
+    After mounting, you should be able to watch (with tcpdump) several
+    RPC READ calls being placed simultaneously.
+
+
+    HOW IT WORKS
+
+    When a process reads from a file on an NFS volume, the following
+    happens:
+
+     *	nfs_file_read sets file->f_reada if more than 1K is
+    	read at once. It then calls generic_file_read.
+
+     *	generic_file_read requests one ore more pages via
+    	nfs_readpage.
+
+     *	nfs_readpage allocates a request slot with an nfsiod
+    	daemon, fills in the READ request, sends out the
+    	RPC call, kicks the daemon, and returns.
+    	If there's no free biod, nfs_readpage places the
+    	call directly, waiting for the reply (sync readpage).
+
+     *	nfsiod calls nfs_rpc_doio to collect the reply. If the
+    	call was successful, it sets page->uptodate and
+    	wakes up all processes waiting on page->wait;
+
+    This is the rough outline only. There are a few things to note:
+
+     *	Async RPC will not be tried when server->rsize < PAGE_SIZE.
+
+     *	When an error occurs, nfsiod has no way of returning
+    	the error code to the user process. Theerefore, it flags
+    	page->error and wakes up all processes waiting on that
+    	page (they usually do so from withing generic_readpage).
+
+    	generic_readpage finds that the page is still not
+    	uptodate, and calls nfs_readpage again. This time around,
+    	nfs_readpage notices that page->error is set and
+    	unconditionally does a synchronous RPC call.
+
+    	This area needs a lot of improvement, since read errors
+    	are not that uncommon (e.g. we have to retransmit calls
+    	if the fsuid is different from the ruid in order to
+    	cope with root squashing and stuff like this).
+
+	Retransmits with fsuid/ruid change should be handled by
+	nfsiod, but this doesn't come easily (a more general nfs_call
+	routine that does all this may be useful...)
+
+     *	To save some time on readaheads, we save one data copy
+    	by frobbing the page into the iovec passed to the
+	RPC code so that the networking layer copies the
+    	data into the page directly.
+
+    	This needs to be adjustable (different authentication
+    	flavors; AUTH_NULL versus AUTH_SHORT verifiers).
+
+     *	Currently, a fixed number of nfsiod's is spawned from
+    	within init_nfs_fs. This is problematic when running
+    	as a loadable module, because this will keep insmod's
+    	memory allocated. As a side-effect, you will see the
+    	nfsiod processes listed as several insmod's when doing
+    	a `ps.'
+
+     * 	This NFS client implements server congestion control via
+	Van Jacobson slow start as implemented in 44BSD. I haven't
+	checked how well this behaves, but since Rick Macklem did
+	it this way, it should be okay :-)
+
+
+    WISH LIST
+
+    After giving this thing some testing, I'd like to add some more
+    features:
+
+     *	Some sort of async write handling. True write-back doesn't
+	work with the current kernel (I think), because invalidate_pages
+	kills all pages, regardless of whether they're dirty or not.
+	Besides, this may require special bdflush treatment because
+	write caching on clients is really hairy.
+
+	Alternatively, a write-through scheme might be useful where
+	the client enqueues the request, but leaves collecting the
+	results to nfsiod. Again, we need a way to pass RPC errors
+	back to the application.
+
+     *	Support for different authentication flavors.
+
+     *	/proc/net/nfsclnt (for nfsstat, etc.).
+
+March 29, 1996
+Olaf Kirch <okir@monad.swb.de>