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path: root/fs/nfs_common/nfslocalio.c
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2025-05-28nfs_localio: change nfsd_file_put_local() to take a pointer to __rcu pointerNeilBrown
Instead of calling xchg() and unrcu_pointer() before nfsd_file_put_local(), we now pass pointer to the __rcu pointer and call xchg() and unrcu_pointer() inside that function. Where unrcu_pointer() is currently called the internals of "struct nfsd_file" are not known and that causes older compilers such as gcc-8 to complain. In some cases we have a __kernel (aka normal) pointer not an __rcu pointer so we need to cast it to __rcu first. This is strictly a weakening so no information is lost. Somewhat surprisingly, this cast is accepted by gcc-8. This has the pleasing result that the cmpxchg() which sets ro_file and rw_file, and also the xchg() which clears them, are both now in the nfsd code. Reported-by: Pali Rohár <pali@kernel.org> Reported-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-05-28nfs_localio: protect race between nfs_uuid_put() and nfs_close_local_fh()NeilBrown
nfs_uuid_put() and nfs_close_local_fh() can race if a "struct nfs_file_localio" is released at the same time that nfsd calls nfs_localio_invalidate_clients(). It is important that neither of these functions completes after the other has started looking at a given nfs_file_localio and before it finishes. If nfs_uuid_put() exits while nfs_close_local_fh() is closing ro_file and rw_file it could return to __nfd_file_cache_purge() while some files are still referenced so the purge may not succeed. If nfs_close_local_fh() exits while nfsd_uuid_put() is still closing the files then the "struct nfs_file_localio" could be freed while nfsd_uuid_put() is still looking at it. This side is currently handled by copying the pointers out of ro_file and rw_file before deleting from the list in nfsd_uuid. We need to preserve this while ensuring that nfsd_uuid_put() does wait for nfs_close_local_fh(). This patch use nfl->uuid and nfl->list to provide the required interlock. nfs_uuid_put() removes the nfs_file_localio from the list, then drops locks and puts the two files, then reclaims the spinlock and sets ->nfs_uuid to NULL. nfs_close_local_fh() operates in the reverse order, setting ->nfs_uuid to NULL, then closing the files, then unlinking from the list. If nfs_uuid_put() finds that ->nfs_uuid is already NULL, it waits for the nfs_file_localio to be removed from the list. If nfs_close_local_fh() find that it has already been unlinked it waits for ->nfs_uuid to become NULL. This ensure that one of the two tries to close the files, but they each waits for the other. As nfs_uuid_put() is making the list empty, change from a list_for_each_safe loop to a while that always takes the first entry. This makes the intent more clear. Also don't move the list to a temporary local list as this would defeat the guarantees required for the interlock. Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-05-28nfs_localio: duplicate nfs_close_local_fh()NeilBrown
nfs_close_local_fh() is called from two different places for quite different use case. It is called from nfs_uuid_put() when the nfs_uuid is being detached - possibly because the nfs server is not longer serving that filesystem. In this case there will always be an nfs_uuid and so rcu_read_lock() is not needed. It is also called when the nfs_file_localio is no longer needed. In this case there may not be an active nfs_uuid. These two can race, and handling the race properly while avoiding excessive locking will require different handling on each side. This patch prepares the way by opencoding nfs_close_local_fh() into nfs_uuid_put(), then simplifying the code there as befits the context. Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-05-28nfs_localio: simplify interface to nfsd for getting nfsd_fileNeilBrown
The nfsd_localio_operations structure contains nfsd_file_get() to get a reference to an nfsd_file. This is only used in one place, where nfsd_open_local_fh() is also used. This patch combines the two, calling nfsd_open_local_fh() passing a pointer to where the nfsd_file pointer might be stored. If there is a pointer there an nfsd_file_get() can get a reference, that reference is returned. If not a new nfsd_file is acquired, stored at the pointer, and returned. When we store a reference we also increase the refcount on the net, as that refcount is decrements when we clear the stored pointer. We now get an extra reference *before* storing the new nfsd_file at the given location. This avoids possible races with the nfsd_file being freed before the final reference can be taken. This patch moves the rcu_dereference() needed after fetching from ro_file or rw_file into the nfsd code where the 'struct nfs_file' is fully defined. This avoids an error reported by older versions of gcc such as gcc-8 which complain about rcu_dereference() use in contexts where the structure (which will supposedly be accessed) is not fully defined. Reported-by: Pali Rohár <pali@kernel.org> Reported-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-05-28nfs_localio: always hold nfsd net ref with nfsd_file refNeilBrown
Having separate nfsd_file_put and nfsd_file_put_local in struct nfsd_localio_operations doesn't make much sense. The difference is that nfsd_file_put doesn't drop a reference to the nfs_net which is what keeps nfsd from shutting down. Currently, if nfsd tries to shutdown it will invalidate the files stored in the list from the nfs_uuid and this will drop all references to the nfsd net that the client holds. But the client could still hold some references to nfsd_files for active IO. So nfsd might think is has completely shut down local IO, but hasn't and has no way to wait for those active IO requests to complete. So this patch changes nfsd_file_get to nfsd_file_get_local and has it increase the ref count on the nfsd net and it replaces all calls to ->nfsd_put_file to ->nfsd_put_file_local. It also changes ->nfsd_open_local_fh to return with the refcount on the net elevated precisely when a valid nfsd_file is returned. This means that whenever the client holds a valid nfsd_file, there will be an associated count on the nfsd net, and so the count can only reach zero when all nfsd_files have been returned. nfs_local_file_put() is changed to call nfs_to_nfsd_file_put_local() instead of replacing calls to one with calls to the other because this will help a later patch which changes nfs_to_nfsd_file_put_local() to take an __rcu pointer while nfs_local_file_put() doesn't. Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-05-28nfs_localio: use cmpxchg() to install new nfs_file_localioNeilBrown
Rather than using nfs_uuid.lock to protect installing a new ro_file or rw_file, change to use cmpxchg(). Removing the file already uses xchg() so this improves symmetry and also makes the code a little simpler. Also remove the optimisation of not taking the lock, and not removing the nfs_file_localio from the linked list, when both ->ro_file and ->rw_file are already NULL. Given that ->nfs_uuid was not NULL, it is extremely unlikely that neither ->ro_file or ->rw_file is NULL so this optimisation can be of little value and it complicates understanding of the code - why can the list_del_init() be skipped? Finally, move the assignment of NULL to ->nfs_uuid until after the last action on the nfs_file_localio (the list_del_init). As soon as this is NULL a racing nfs_close_local_fh() can bypass all the locking and go on to free the nfs_file_localio, so we must be certain to be finished with it first. Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs: probe for LOCALIO when v3 client reconnects to serverMike Snitzer
Re-enabling NFSv3 LOCALIO is made more complex (than NFSv4) because v3 is stateless. As such, the hueristic used to identify a LOCALIO probe point is more adhoc by nature: if/when NFSv3 client IO begins to complete again in terms of normal RPC-based NFSv3 server IO, attempt nfs_local_probe_async(). Care is taken to throttle the frequency of nfs_local_probe_async(), otherwise there could be a flood of repeat calls to nfs_local_probe_async(). The throttle is admin controlled using a new module parameter for nfsv3, e.g.: echo 512 > /sys/module/nfsv3/parameters/nfs3_localio_probe_throttle Probe for NFSv3 LOCALIO every N IO requests (512 in this case). Must be power-of-2, defaults to 0 (probing disabled). On systems that expect to use LOCALIO with NFSv3 the admin should configure the 'nfs3_localio_probe_throttle' module parameter. This commit backfills module parameter documentation in localio.rst Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs/localio: remove redundant code and simplify LOCALIO enablementMike Snitzer
Remove nfs_local_enable and nfs_local_disable, instead use nfs_localio_enable_client and nfs_localio_disable_client. Discontinue use of the NFS_CS_LOCAL_IO bit in the nfs_client struct's cl_flags to reflect that LOCALIO is enabled; instead just test if the net member of the nfs_uuid_t struct is set. Also remove NFS_CS_LOCAL_IO. Lastly, remove trace_nfs_local_enable and trace_nfs_local_disable because comparable traces are available from nfs_localio.ko. Suggested-by: NeilBrown <neilb@suse.de> Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs_common: add nfs_localio trace eventsMike Snitzer
The nfs_localio.ko now exposes /sys/kernel/tracing/events/nfs_localio with nfs_localio_enable_client and nfs_localio_disable_client events. Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs_common: track all open nfsd_files per LOCALIO nfs_clientMike Snitzer
This tracking enables __nfsd_file_cache_purge() to call nfs_localio_invalidate_clients(), upon shutdown or export change, to nfs_close_local_fh() all open nfsd_files that are still cached by the LOCALIO nfs clients associated with nfsd_net that is being shutdown. Now that the client must track all open nfsd_files there was more work than necessary being done with the global nfs_uuids_lock contended. This manifested in various RCU issues, e.g.: hrtimer: interrupt took 47969440 ns rcu: INFO: rcu_sched detected stalls on CPUs/tasks: Use nfs_uuid->lock to protect all nfs_uuid_t members, instead of nfs_uuids_lock, once nfs_uuid_is_local() adds the client to nn->local_clients. Also add 'local_clients_lock' to 'struct nfsd_net' to protect nn->local_clients. And store a pointer to spinlock in the 'list_lock' member of nfs_uuid_t so nfs_localio_disable_client() can use it to avoid taking the global nfs_uuids_lock. In combination, these split out locks eliminate the use of the single nfslocalio.c global nfs_uuids_lock in the IO paths (open and close). Also refactored associated fs/nfs_common/nfslocalio.c methods' locking to reduce work performed with spinlocks held in general. Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs_common: rename nfslocalio nfs_uuid_lock to nfs_uuids_lockMike Snitzer
This global spinlock protects all nfs_uuid_t relative to the global nfs_uuids list. A later commit will split this global spinlock so prepare by renaming this lock to reflect its intended narrow scope. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfsd: rename nfsd_serv_ prefixed methods and variables with nfsd_net_Mike Snitzer
Also update Documentation/filesystems/nfs/localio.rst accordingly and reduce the technical documentation debt that was previously captured in that document. Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Acked-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs: cache all open LOCALIO nfsd_file(s) in clientMike Snitzer
This commit switches from leaning heavily on NFSD's filecache (in terms of GC'd nfsd_files) back to caching nfsd_files in the client. A later commit will add the callback mechanism needed to allow NFSD to force the NFS client to cleanup all cached nfsd_files. Add nfs_fh_localio_init() and 'struct nfs_fh_localio' to cache opened nfsd_file(s) (both a RO and RW nfsd_file is able to be opened and cached for a given nfs_fh). Update nfs_local_open_fh() to cache the nfsd_file once it is opened using __nfs_local_open_fh(). Introduce nfs_close_local_fh() to clear the cached open nfsd_files and call nfs_to_nfsd_file_put_local(). Refcounting is such that: - nfs_local_open_fh() is paired with nfs_close_local_fh(). - __nfs_local_open_fh() is paired with nfs_to_nfsd_file_put_local(). - nfs_local_file_get() is paired with nfs_local_file_put(). Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs_common: move localio_lock to new lock member of nfs_uuid_tMike Snitzer
Remove cl_localio_lock from 'struct nfs_client' in favor of adding a lock to the nfs_uuid_t struct (which is embedded in each nfs_client). Push nfs_local_{enable,disable} implementation down to nfs_common. Those methods now call nfs_localio_{enable,disable}_client. This allows implementing nfs_localio_invalidate_clients in terms of nfs_localio_disable_client. Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2025-01-14nfs_common: rename functions that invalidate LOCALIO nfs_clientsMike Snitzer
Rename nfs_uuid_invalidate_one_client to nfs_localio_disable_client. Rename nfs_uuid_invalidate_clients to nfs_localio_invalidate_clients. Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: NeilBrown <neilb@suse.de> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2024-11-18nfs_common: must not hold RCU while calling nfsd_file_put_localMike Snitzer
Move holding the RCU from nfs_to_nfsd_file_put_local to nfs_to_nfsd_net_put. It is the call to nfs_to->nfsd_serv_put that requires the RCU anyway (the puts for nfsd_file and netns were combined to avoid an extra indirect reference but that micro-optimization isn't possible now). This fixes xfstests generic/013 and it triggering: "Voluntary context switch within RCU read-side critical section!" [ 143.545738] Call Trace: [ 143.546206] <TASK> [ 143.546625] ? show_regs+0x6d/0x80 [ 143.547267] ? __warn+0x91/0x140 [ 143.547951] ? rcu_note_context_switch+0x496/0x5d0 [ 143.548856] ? report_bug+0x193/0x1a0 [ 143.549557] ? handle_bug+0x63/0xa0 [ 143.550214] ? exc_invalid_op+0x1d/0x80 [ 143.550938] ? asm_exc_invalid_op+0x1f/0x30 [ 143.551736] ? rcu_note_context_switch+0x496/0x5d0 [ 143.552634] ? wakeup_preempt+0x62/0x70 [ 143.553358] __schedule+0xaa/0x1380 [ 143.554025] ? _raw_spin_unlock_irqrestore+0x12/0x40 [ 143.554958] ? try_to_wake_up+0x1fe/0x6b0 [ 143.555715] ? wake_up_process+0x19/0x20 [ 143.556452] schedule+0x2e/0x120 [ 143.557066] schedule_preempt_disabled+0x19/0x30 [ 143.557933] rwsem_down_read_slowpath+0x24d/0x4a0 [ 143.558818] ? xfs_efi_item_format+0x50/0xc0 [xfs] [ 143.559894] down_read+0x4e/0xb0 [ 143.560519] xlog_cil_commit+0x1b2/0xbc0 [xfs] [ 143.561460] ? _raw_spin_unlock+0x12/0x30 [ 143.562212] ? xfs_inode_item_precommit+0xc7/0x220 [xfs] [ 143.563309] ? xfs_trans_run_precommits+0x69/0xd0 [xfs] [ 143.564394] __xfs_trans_commit+0xb5/0x330 [xfs] [ 143.565367] xfs_trans_roll+0x48/0xc0 [xfs] [ 143.566262] xfs_defer_trans_roll+0x57/0x100 [xfs] [ 143.567278] xfs_defer_finish_noroll+0x27a/0x490 [xfs] [ 143.568342] xfs_defer_finish+0x1a/0x80 [xfs] [ 143.569267] xfs_bunmapi_range+0x4d/0xb0 [xfs] [ 143.570208] xfs_itruncate_extents_flags+0x13d/0x230 [xfs] [ 143.571353] xfs_free_eofblocks+0x12e/0x190 [xfs] [ 143.572359] xfs_file_release+0x12d/0x140 [xfs] [ 143.573324] __fput+0xe8/0x2d0 [ 143.573922] __fput_sync+0x1d/0x30 [ 143.574574] nfsd_filp_close+0x33/0x60 [nfsd] [ 143.575430] nfsd_file_free+0x96/0x150 [nfsd] [ 143.576274] nfsd_file_put+0xf7/0x1a0 [nfsd] [ 143.577104] nfsd_file_put_local+0x18/0x30 [nfsd] [ 143.578070] nfs_close_local_fh+0x101/0x110 [nfs_localio] [ 143.579079] __put_nfs_open_context+0xc9/0x180 [nfs] [ 143.580031] nfs_file_clear_open_context+0x4a/0x60 [nfs] [ 143.581038] nfs_file_release+0x3e/0x60 [nfs] [ 143.581879] __fput+0xe8/0x2d0 [ 143.582464] __fput_sync+0x1d/0x30 [ 143.583108] __x64_sys_close+0x41/0x80 [ 143.583823] x64_sys_call+0x189a/0x20d0 [ 143.584552] do_syscall_64+0x64/0x170 [ 143.585240] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 143.586185] RIP: 0033:0x7f3c5153efd7 Fixes: 65f2a5c36635 ("nfs_common: fix race in NFS calls to nfsd_file_put_local() and nfsd_serv_put()") Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: NeilBrown <neilb@suse.de> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2024-11-04nfs_common: fix localio to cope with racing nfs_local_probe()Mike Snitzer
Fix the possibility of racing nfs_local_probe() resulting in: list_add double add: new=ffff8b99707f9f58, prev=ffff8b99707f9f58, next=ffffffffc0f30000. ------------[ cut here ]------------ kernel BUG at lib/list_debug.c:35! Add nfs_uuid_init() to properly initialize all nfs_uuid_t members (particularly its list_head). Switch to returning bool from nfs_uuid_begin(), returns false if nfs_uuid_t is already in-use (its list_head is on a list). Update nfs_local_probe() to return early if the nfs_client's cl_uuid (nfs_uuid_t) is in-use. Also, switch nfs_uuid_begin() from using list_add_tail_rcu() to list_add_tail() -- rculist was used in an earlier version of the localio code that had a lockless nfs_uuid_lookup interface. Signed-off-by: Mike Snitzer <snitzer@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2024-10-03nfs_common: fix race in NFS calls to nfsd_file_put_local() and nfsd_serv_put()Mike Snitzer
Add nfs_to_nfsd_file_put_local() interface to fix race with nfsd module unload. Similarly, use RCU around nfs_open_local_fh()'s error path call to nfs_to->nfsd_serv_put(). Holding RCU ensures that NFS will safely _call and return_ from its nfs_to calls into the NFSD functions nfsd_file_put_local() and nfsd_serv_put(). Otherwise, if RCU isn't used then there is a narrow window when NFS's reference for the nfsd_file and nfsd_serv are dropped and the NFSD module could be unloaded, which could result in a crash from the return instruction for either nfs_to->nfsd_file_put_local() or nfs_to->nfsd_serv_put(). Reported-by: NeilBrown <neilb@suse.de> Signed-off-by: Mike Snitzer <snitzer@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2024-09-23nfs: add LOCALIO supportWeston Andros Adamson
Add client support for bypassing NFS for localhost reads, writes, and commits. This is only useful when the client and the server are running on the same host. nfs_local_probe() is stubbed out, later commits will enable client and server handshake via a Linux-only LOCALIO auxiliary RPC protocol. This has dynamic binding with the nfsd module (via nfs_localio module which is part of nfs_common). LOCALIO will only work if nfsd is already loaded. The "localio_enabled" nfs kernel module parameter can be used to disable and enable the ability to use LOCALIO support. CONFIG_NFS_LOCALIO enables NFS client support for LOCALIO. Lastly, LOCALIO uses an nfsd_file to initiate all IO. To make proper use of nfsd_file (and nfsd's filecache) its lifetime (duration before nfsd_file_put is called) must extend until after commit, read and write operations. So rather than immediately drop the nfsd_file reference in nfs_local_open_fh(), that doesn't happen until nfs_local_pgio_release() for read/write and not until nfs_local_release_commit_data() for commit. The same applies to the reference held on nfsd's nn->nfsd_serv. Both objects' lifetimes and associated references are managed through calls to nfs_to->nfsd_file_put_local(). Signed-off-by: Weston Andros Adamson <dros@primarydata.com> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> Co-developed-by: Mike Snitzer <snitzer@kernel.org> Signed-off-by: Mike Snitzer <snitzer@kernel.org> Signed-off-by: NeilBrown <neilb@suse.de> # nfs_open_local_fh Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2024-09-23nfs_common: prepare for the NFS client to use nfsd_file for LOCALIOMike Snitzer
The next commit will introduce nfsd_open_local_fh() which returns an nfsd_file structure. This commit exposes LOCALIO's required NFSD symbols to the NFS client: - Make nfsd_open_local_fh() symbol and other required NFSD symbols available to NFS in a global 'nfs_to' nfsd_localio_operations struct (global access suggested by Trond, nfsd_localio_operations suggested by NeilBrown). The next commit will also introduce nfsd_localio_ops_init() that init_nfsd() will call to initialize 'nfs_to'. - Introduce nfsd_file_file() that provides access to nfsd_file's backing file. Keeps nfsd_file structure opaque to NFS client (as suggested by Jeff Layton). - Introduce nfsd_file_put_local() that will put the reference to the nfsd_file's associated nn->nfsd_serv and then put the reference to the nfsd_file (as suggested by NeilBrown). Suggested-by: Trond Myklebust <trond.myklebust@hammerspace.com> # nfs_to Suggested-by: NeilBrown <neilb@suse.de> # nfsd_localio_operations Suggested-by: Jeff Layton <jlayton@kernel.org> # nfsd_file_file Signed-off-by: Mike Snitzer <snitzer@kernel.org> Reviewed-by: NeilBrown <neilb@suse.de> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
2024-09-23nfs_common: add NFS LOCALIO auxiliary protocol enablementMike Snitzer
fs/nfs_common/nfslocalio.c provides interfaces that enable an NFS client to generate a nonce (single-use UUID) and associated nfs_uuid_t struct, register it with nfs_common for subsequent lookup and verification by the NFS server and if matched the NFS server populates members in the nfs_uuid_t struct. nfs_common's nfs_uuids list is the basis for localio enablement, as such it has members that point to nfsd memory for direct use by the client (e.g. 'net' is the server's network namespace, through it the client can access nn->nfsd_serv). This commit also provides the base nfs_uuid_t interfaces to allow proper net namespace refcounting for the LOCALIO use case. CONFIG_NFS_LOCALIO controls the nfs_common, NFS server and NFS client enablement for LOCALIO. If both NFS_FS=m and NFSD=m then NFS_COMMON_LOCALIO_SUPPORT=m and nfs_localio.ko is built (and provides nfs_common's LOCALIO support). # lsmod | grep nfs_localio nfs_localio 12288 2 nfsd,nfs sunrpc 745472 35 nfs_localio,nfsd,auth_rpcgss,lockd,nfsv3,nfs Signed-off-by: Mike Snitzer <snitzer@kernel.org> Co-developed-by: NeilBrown <neilb@suse.de> Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>