The NFS client's a_ops->direct_IO method, nfs_direct_IO, is required to
be present to allow NFS files to be opened with O_DIRECT, but is never
called because the NFS client shunts reads and writes to files opened
with O_DIRECT directly to its own routines.

Gut the nfs_direct_IO function.  This eliminates the only part of the
NFS client's direct I/O path that requires support for multi-segment
iovs, allowing further simplification in subsequent patches.

Test plan:
Compile the kernel with CONFIG_NFS and CONFIG_NFS_DIRECTIO enabled.  Millions
of fsx-odirect ops.  OraSim.
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

Same callback hierarchy inversion as for the NFS write calls. This patch is
not strictly speaking needed by the O_DIRECT code, but avoids confusing
differences between the asynchronous read and write code.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

Invoke the byte and event counter macros where we want to count bytes and
events.

Clean-up: fix a possible NULL dereference in nfs_lock, and simplify
nfs_file_open.

Test-plan:
fsx and iozone on UP and SMP systems, with and without pre-emption.  Watch
for memory overwrite bugs, and performance loss (significantly more CPU
required per op).
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

Based on an original patch by Mike O'Connor and Greg Banks of SGI.

Mike states:

A normal user can panic an NFS client and cause a local DoS with
'judicious'(?) use of O_DIRECT.  Any O_DIRECT write to an NFS file where the
user buffer starts with a valid mapped page and contains an unmapped page,
will crash in this way.  I haven't followed the code, but O_DIRECT reads with
similar user buffers will probably also crash albeit in different ways.

Details: when nfs_get_user_pages() calls get_user_pages(), it detects and
correctly handles get_user_pages() returning an error, which happens if the
first page covered by the user buffer's address range is unmapped.  However,
if the first page is mapped but some subsequent page isn't, get_user_pages()
will return a positive number which is less than the number of pages requested
(this behaviour is sort of analagous to a short write() call and appears to be
intentional).  nfs_get_user_pages() doesn't detect this and hands off the
array of pages (whose last few elements are random rubbish from the newly
allocated array memory) to it's caller, whence they go to
nfs_direct_write_seg(), which then totally ignores the nr_pages it's given,
and calculates its own idea of how many pages are in the array from the user
buffer length.  Needless to say, when it comes to transmit those uninitialised
page* pointers, we see a crash in the network stack.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

 Only do a sync_retry if the memcmp failed.
Signed-off-by: NDirk Mueller <dmueller@suse.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 ...and avoid calling set_page_dirty on them
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 Most NFS server implementations allow up to 64KB reads and writes on the
 wire.  The Solaris NFS server allows up to a megabyte, for instance.

 Now the Linux NFS client supports transfer sizes up to 1MB, too.  This will
 help reduce protocol and context switch overhead on read/write intensive NFS
 workloads, and support larger atomic read and write operations on servers
 that support them.

 Test-plan:
 Connectathon and iozone on mount point with wsize=rsize>32768 over TCP.
 Tests with NFS over UDP to verify the maximum RPC payload size cap.
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 Replace ad hoc write parameter sanity checking in nfs_file_direct_write()
 with a call to generic_write_checks().  This should make the proper checks
 modulo the O_LARGEFILE flag, and should catch NFSv2-specific limitations by
 virtue of i_sb->s_maxbytes.

 Test plan:
 Posix compliance testing with both NFSv2 and NFSv3.
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 The NFSv4 model requires us to complete all RPC calls that might
 establish state on the server whether or not the user wants to
 interrupt it. We may also need to schedule new work (including
 new RPC calls) in order to cancel the new state.

 The asynchronous RPC model will allow us to ensure that RPC calls
 always complete, but in order to allow for "synchronous" RPC, we
 want to add the ability to wait for completion.
 The waits are, of course, interruptible.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 Shrink the RPC task structure. Instead of storing separate pointers
 for task->tk_exit and task->tk_release, put them in a structure.

 Also pass the user data pointer as a parameter instead of passing it via
 task->tk_calldata. This enables us to nest callbacks.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 Ensure we call unmap_mapping_range() and sync dirty pages to disk before
 doing an NFS direct write.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

 Fix some dprintk's so that NLM, NFS client, and RPC client compile
 cleanly if CONFIG_SYSCTL is disabled.

 Test plan:
 Compile kernel with CONFIG_NFS enabled and CONFIG_SYSCTL disabled.
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

The following patch removes the f_error field and all checks of f_error.

Trond said:

  f_error was introduced for NFS, and made sense when we were guaranteed
  always to have a file pointer around when write errors occurred.  Since
  then, we have (for various reasons) had to introduce the nfs_open_context in
  order to track the file read/write state, and it made sense to move our
  f_error tracking there too.
Signed-off-by: NChristoph Lameter <christoph@lameter.com>
Acked-by: NTrond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

 Instead of looking at whether or not the file is open for writes before
 we accept to update the length using the server value, we should rather
 be looking at whether or not we are currently caching any writes.

 Failure to do so means in particular that we're not updating the file
 length correctly after obtaining a POSIX or BSD lock.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!