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100ccd18bb
Track the file position above which the server is not expected to have any
data (the "zero point") and preemptively assume that we can satisfy
requests by filling them with zeroes locally rather than attempting to
download them if they're over that line - even if we've written data back
to the server. Assume that any data that was written back above that
position is held in the local cache. Note that we have to split requests
that straddle the line.
Make use of this to optimise away some reads from the server. We need to
set the zero point in the following circumstances:
(1) When we see an extant remote inode and have no cache for it, we set
the zero_point to i_size.
(2) On local inode creation, we set zero_point to 0.
(3) On local truncation down, we reduce zero_point to the new i_size if
the new i_size is lower.
(4) On local truncation up, we don't change zero_point.
(5) On local modification, we don't change zero_point.
(6) On remote invalidation, we set zero_point to the new i_size.
(7) If stored data is discarded from the pagecache or culled from fscache,
we must set zero_point above that if the data also got written to the
server.
(8) If dirty data is written back to the server, but not fscache, we must
set zero_point above that.
(9) If a direct I/O write is made, set zero_point above that.
Assuming the above, any read from the server at or above the zero_point
position will return all zeroes.
The zero_point value can be stored in the cache, provided the above rules
are applied to it by any code that culls part of the local cache.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
203 lines
6.5 KiB
C
203 lines
6.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/* NFS filesystem cache interface definitions
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*
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* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#ifndef _NFS_FSCACHE_H
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#define _NFS_FSCACHE_H
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#include <linux/swap.h>
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#include <linux/nfs_fs.h>
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#include <linux/nfs_mount.h>
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#include <linux/nfs4_mount.h>
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#include <linux/fscache.h>
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#include <linux/iversion.h>
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#ifdef CONFIG_NFS_FSCACHE
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/*
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* Definition of the auxiliary data attached to NFS inode storage objects
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* within the cache.
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*
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* The contents of this struct are recorded in the on-disk local cache in the
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* auxiliary data attached to the data storage object backing an inode. This
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* permits coherency to be managed when a new inode binds to an already extant
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* cache object.
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*/
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struct nfs_fscache_inode_auxdata {
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s64 mtime_sec;
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s64 mtime_nsec;
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s64 ctime_sec;
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s64 ctime_nsec;
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u64 change_attr;
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};
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struct nfs_netfs_io_data {
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/*
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* NFS may split a netfs_io_subrequest into multiple RPCs, each
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* with their own read completion. In netfs, we can only call
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* netfs_subreq_terminated() once for each subrequest. Use the
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* refcount here to double as a marker of the last RPC completion,
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* and only call netfs via netfs_subreq_terminated() once.
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*/
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refcount_t refcount;
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struct netfs_io_subrequest *sreq;
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/*
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* Final disposition of the netfs_io_subrequest, sent in
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* netfs_subreq_terminated()
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*/
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atomic64_t transferred;
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int error;
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};
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static inline void nfs_netfs_get(struct nfs_netfs_io_data *netfs)
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{
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refcount_inc(&netfs->refcount);
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}
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static inline void nfs_netfs_put(struct nfs_netfs_io_data *netfs)
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{
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ssize_t final_len;
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/* Only the last RPC completion should call netfs_subreq_terminated() */
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if (!refcount_dec_and_test(&netfs->refcount))
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return;
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/*
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* The NFS pageio interface may read a complete page, even when netfs
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* only asked for a partial page. Specifically, this may be seen when
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* one thread is truncating a file while another one is reading the last
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* page of the file.
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* Correct the final length here to be no larger than the netfs subrequest
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* length, and thus avoid netfs's "Subreq overread" warning message.
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*/
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final_len = min_t(s64, netfs->sreq->len, atomic64_read(&netfs->transferred));
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netfs_subreq_terminated(netfs->sreq, netfs->error ?: final_len, false);
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kfree(netfs);
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}
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static inline void nfs_netfs_inode_init(struct nfs_inode *nfsi)
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{
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netfs_inode_init(&nfsi->netfs, &nfs_netfs_ops, false);
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}
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extern void nfs_netfs_initiate_read(struct nfs_pgio_header *hdr);
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extern void nfs_netfs_read_completion(struct nfs_pgio_header *hdr);
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extern int nfs_netfs_folio_unlock(struct folio *folio);
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/*
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* fscache.c
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*/
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extern int nfs_fscache_get_super_cookie(struct super_block *, const char *, int);
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extern void nfs_fscache_release_super_cookie(struct super_block *);
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extern void nfs_fscache_init_inode(struct inode *);
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extern void nfs_fscache_clear_inode(struct inode *);
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extern void nfs_fscache_open_file(struct inode *, struct file *);
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extern void nfs_fscache_release_file(struct inode *, struct file *);
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extern int nfs_netfs_readahead(struct readahead_control *ractl);
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extern int nfs_netfs_read_folio(struct file *file, struct folio *folio);
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static inline bool nfs_fscache_release_folio(struct folio *folio, gfp_t gfp)
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{
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if (folio_test_fscache(folio)) {
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if (current_is_kswapd() || !(gfp & __GFP_FS))
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return false;
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folio_wait_fscache(folio);
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}
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fscache_note_page_release(netfs_i_cookie(netfs_inode(folio->mapping->host)));
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return true;
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}
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static inline void nfs_fscache_update_auxdata(struct nfs_fscache_inode_auxdata *auxdata,
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struct inode *inode)
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{
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memset(auxdata, 0, sizeof(*auxdata));
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auxdata->mtime_sec = inode_get_mtime(inode).tv_sec;
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auxdata->mtime_nsec = inode_get_mtime(inode).tv_nsec;
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auxdata->ctime_sec = inode_get_ctime(inode).tv_sec;
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auxdata->ctime_nsec = inode_get_ctime(inode).tv_nsec;
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if (NFS_SERVER(inode)->nfs_client->rpc_ops->version == 4)
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auxdata->change_attr = inode_peek_iversion_raw(inode);
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}
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/*
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* Invalidate the contents of fscache for this inode. This will not sleep.
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*/
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static inline void nfs_fscache_invalidate(struct inode *inode, int flags)
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{
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struct nfs_fscache_inode_auxdata auxdata;
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struct fscache_cookie *cookie = netfs_i_cookie(&NFS_I(inode)->netfs);
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nfs_fscache_update_auxdata(&auxdata, inode);
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fscache_invalidate(cookie, &auxdata, i_size_read(inode), flags);
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}
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/*
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* indicate the client caching state as readable text
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*/
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static inline const char *nfs_server_fscache_state(struct nfs_server *server)
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{
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if (server->fscache)
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return "yes";
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return "no ";
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}
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static inline void nfs_netfs_set_pgio_header(struct nfs_pgio_header *hdr,
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struct nfs_pageio_descriptor *desc)
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{
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hdr->netfs = desc->pg_netfs;
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}
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static inline void nfs_netfs_set_pageio_descriptor(struct nfs_pageio_descriptor *desc,
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struct nfs_pgio_header *hdr)
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{
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desc->pg_netfs = hdr->netfs;
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}
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static inline void nfs_netfs_reset_pageio_descriptor(struct nfs_pageio_descriptor *desc)
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{
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desc->pg_netfs = NULL;
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}
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#else /* CONFIG_NFS_FSCACHE */
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static inline void nfs_netfs_inode_init(struct nfs_inode *nfsi) {}
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static inline void nfs_netfs_initiate_read(struct nfs_pgio_header *hdr) {}
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static inline void nfs_netfs_read_completion(struct nfs_pgio_header *hdr) {}
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static inline int nfs_netfs_folio_unlock(struct folio *folio)
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{
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return 1;
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}
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static inline void nfs_fscache_release_super_cookie(struct super_block *sb) {}
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static inline void nfs_fscache_init_inode(struct inode *inode) {}
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static inline void nfs_fscache_clear_inode(struct inode *inode) {}
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static inline void nfs_fscache_open_file(struct inode *inode,
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struct file *filp) {}
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static inline void nfs_fscache_release_file(struct inode *inode, struct file *file) {}
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static inline int nfs_netfs_readahead(struct readahead_control *ractl)
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{
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return -ENOBUFS;
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}
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static inline int nfs_netfs_read_folio(struct file *file, struct folio *folio)
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{
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return -ENOBUFS;
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}
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static inline bool nfs_fscache_release_folio(struct folio *folio, gfp_t gfp)
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{
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return true; /* may release folio */
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}
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static inline void nfs_fscache_invalidate(struct inode *inode, int flags) {}
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static inline const char *nfs_server_fscache_state(struct nfs_server *server)
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{
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return "no ";
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}
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static inline void nfs_netfs_set_pgio_header(struct nfs_pgio_header *hdr,
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struct nfs_pageio_descriptor *desc) {}
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static inline void nfs_netfs_set_pageio_descriptor(struct nfs_pageio_descriptor *desc,
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struct nfs_pgio_header *hdr) {}
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static inline void nfs_netfs_reset_pageio_descriptor(struct nfs_pageio_descriptor *desc) {}
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#endif /* CONFIG_NFS_FSCACHE */
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#endif /* _NFS_FSCACHE_H */
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