Merge tag 'nfsd-5.16' of git://linux-nfs.org/~bfields/linux

Pull nfsd updates from Bruce Fields:
 "A slow cycle for nfsd: mainly cleanup, including Neil's patch dropping
  support for a filehandle format deprecated 20 years ago, and further
  xdr-related cleanup from Chuck"

* tag 'nfsd-5.16' of git://linux-nfs.org/~bfields/linux: (26 commits)
  nfsd4: remove obselete comment
  nfsd: document server-to-server-copy parameters
  NFSD:fix boolreturn.cocci warning
  nfsd: update create verifier comment
  SUNRPC: Change return value type of .pc_encode
  SUNRPC: Replace the "__be32 *p" parameter to .pc_encode
  NFSD: Save location of NFSv4 COMPOUND status
  SUNRPC: Change return value type of .pc_decode
  SUNRPC: Replace the "__be32 *p" parameter to .pc_decode
  SUNRPC: De-duplicate .pc_release() call sites
  SUNRPC: Simplify the SVC dispatch code path
  SUNRPC: Capture value of xdr_buf::page_base
  SUNRPC: Add trace event when alloc_pages_bulk() makes no progress
  svcrdma: Split svcrmda_wc_{read,write} tracepoints
  svcrdma: Split the svcrdma_wc_send() tracepoint
  svcrdma: Split the svcrdma_wc_receive() tracepoint
  NFSD: Have legacy NFSD WRITE decoders use xdr_stream_subsegment()
  SUNRPC: xdr_stream_subsegment() must handle non-zero page_bases
  NFSD: Initialize pointer ni with NULL and not plain integer 0
  NFSD: simplify struct nfsfh
  ...

3 files changed, 128 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f65b95993228..9725c546a0d4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3253,6 +3253,19 @@
 			driver. A non-zero value sets the minimum interval
 			in seconds between layoutstats transmissions.
 
+	nfsd.inter_copy_offload_enable =
+			[NFSv4.2] When set to 1, the server will support
+			server-to-server copies for which this server is
+			the destination of the copy.
+
+	nfsd.nfsd4_ssc_umount_timeout =
+			[NFSv4.2] When used as the destination of a
+			server-to-server copy, knfsd temporarily mounts
+			the source server.  It caches the mount in case
+			it will be needed again, and discards it if not
+			used for the number of milliseconds specified by
+			this parameter.
+
 	nfsd.nfs4_disable_idmapping=
 			[NFSv4] When set to the default of '1', the NFSv4
 			server will return only numeric uids and gids to
@@ -3260,6 +3273,7 @@
 			and gids from such clients.  This is intended to ease
 			migration from NFSv2/v3.
 
+
 	nmi_backtrace.backtrace_idle [KNL]
 			Dump stacks even of idle CPUs in response to an
 			NMI stack-backtrace request.
diff --git a/Documentation/filesystems/nfs/index.rst b/Documentation/filesystems/nfs/index.rst
index 65805624e39b..288d8ddb2bc6 100644
--- a/Documentation/filesystems/nfs/index.rst
+++ b/Documentation/filesystems/nfs/index.rst
@@ -11,3 +11,4 @@ NFS
    rpc-server-gss
    nfs41-server
    knfsd-stats
+   reexport
diff --git a/Documentation/filesystems/nfs/reexport.rst b/Documentation/filesystems/nfs/reexport.rst
new file mode 100644
index 000000000000..ff9ae4a46530
--- /dev/null
+++ b/Documentation/filesystems/nfs/reexport.rst
@@ -0,0 +1,113 @@
+Reexporting NFS filesystems
+===========================
+
+Overview
+--------
+
+It is possible to reexport an NFS filesystem over NFS.  However, this
+feature comes with a number of limitations.  Before trying it, we
+recommend some careful research to determine whether it will work for
+your purposes.
+
+A discussion of current known limitations follows.
+
+"fsid=" required, crossmnt broken
+---------------------------------
+
+We require the "fsid=" export option on any reexport of an NFS
+filesystem.  You can use "uuidgen -r" to generate a unique argument.
+
+The "crossmnt" export does not propagate "fsid=", so it will not allow
+traversing into further nfs filesystems; if you wish to export nfs
+filesystems mounted under the exported filesystem, you'll need to export
+them explicitly, assigning each its own unique "fsid= option.
+
+Reboot recovery
+---------------
+
+The NFS protocol's normal reboot recovery mechanisms don't work for the
+case when the reexport server reboots.  Clients will lose any locks
+they held before the reboot, and further IO will result in errors.
+Closing and reopening files should clear the errors.
+
+Filehandle limits
+-----------------
+
+If the original server uses an X byte filehandle for a given object, the
+reexport server's filehandle for the reexported object will be X+22
+bytes, rounded up to the nearest multiple of four bytes.
+
+The result must fit into the RFC-mandated filehandle size limits:
+
++-------+-----------+
+| NFSv2 |  32 bytes |
++-------+-----------+
+| NFSv3 |  64 bytes |
++-------+-----------+
+| NFSv4 | 128 bytes |
++-------+-----------+
+
+So, for example, you will only be able to reexport a filesystem over
+NFSv2 if the original server gives you filehandles that fit in 10
+bytes--which is unlikely.
+
+In general there's no way to know the maximum filehandle size given out
+by an NFS server without asking the server vendor.
+
+But the following table gives a few examples.  The first column is the
+typical length of the filehandle from a Linux server exporting the given
+filesystem, the second is the length after that nfs export is reexported
+by another Linux host:
+
++--------+-------------------+----------------+
+|        | filehandle length | after reexport |
++========+===================+================+
+| ext4:  | 28 bytes          | 52 bytes       |
++--------+-------------------+----------------+
+| xfs:   | 32 bytes          | 56 bytes       |
++--------+-------------------+----------------+
+| btrfs: | 40 bytes          | 64 bytes       |
++--------+-------------------+----------------+
+
+All will therefore fit in an NFSv3 or NFSv4 filehandle after reexport,
+but none are reexportable over NFSv2.
+
+Linux server filehandles are a bit more complicated than this, though;
+for example:
+
+        - The (non-default) "subtreecheck" export option generally
+          requires another 4 to 8 bytes in the filehandle.
+        - If you export a subdirectory of a filesystem (instead of
+          exporting the filesystem root), that also usually adds 4 to 8
+          bytes.
+        - If you export over NFSv2, knfsd usually uses a shorter
+          filesystem identifier that saves 8 bytes.
+        - The root directory of an export uses a filehandle that is
+          shorter.
+
+As you can see, the 128-byte NFSv4 filehandle is large enough that
+you're unlikely to have trouble using NFSv4 to reexport any filesystem
+exported from a Linux server.  In general, if the original server is
+something that also supports NFSv3, you're *probably* OK.  Re-exporting
+over NFSv3 may be dicier, and reexporting over NFSv2 will probably
+never work.
+
+For more details of Linux filehandle structure, the best reference is
+the source code and comments; see in particular:
+
+        - include/linux/exportfs.h:enum fid_type
+        - include/uapi/linux/nfsd/nfsfh.h:struct nfs_fhbase_new
+        - fs/nfsd/nfsfh.c:set_version_and_fsid_type
+        - fs/nfs/export.c:nfs_encode_fh
+
+Open DENY bits ignored
+----------------------
+
+NFS since NFSv4 supports ALLOW and DENY bits taken from Windows, which
+allow you, for example, to open a file in a mode which forbids other
+read opens or write opens. The Linux client doesn't use them, and the
+server's support has always been incomplete: they are enforced only
+against other NFS users, not against processes accessing the exported
+filesystem locally. A reexport server will also not pass them along to
+the original server, so they will not be enforced between clients of
+different reexport servers.