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![David Howells](/assets/img/avatar_default.png)
Use i_writecount to control whether to get an fscache cookie in nfs_open() as NFS does not do write caching yet. I *think* this is the cause of a problem encountered by Mark Moseley whereby __fscache_uncache_page() gets a NULL pointer dereference because cookie->def is NULL: BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 IP: [<ffffffff812a1903>] __fscache_uncache_page+0x23/0x160 PGD 0 Thread overran stack, or stack corrupted Oops: 0000 [#1] SMP Modules linked in: ... CPU: 7 PID: 18993 Comm: php Not tainted 3.11.1 #1 Hardware name: Dell Inc. PowerEdge R420/072XWF, BIOS 1.3.5 08/21/2012 task: ffff8804203460c0 ti: ffff880420346640 RIP: 0010:[<ffffffff812a1903>] __fscache_uncache_page+0x23/0x160 RSP: 0018:ffff8801053af878 EFLAGS: 00210286 RAX: 0000000000000000 RBX: ffff8800be2f8780 RCX: ffff88022ffae5e8 RDX: 0000000000004c66 RSI: ffffea00055ff440 RDI: ffff8800be2f8780 RBP: ffff8801053af898 R08: 0000000000000001 R09: 0000000000000003 R10: 0000000000000000 R11: 0000000000000000 R12: ffffea00055ff440 R13: 0000000000001000 R14: ffff8800c50be538 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff88042fc60000(0063) knlGS:00000000e439c700 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 0000000000000010 CR3: 0000000001d8f000 CR4: 00000000000607f0 Stack: ... Call Trace: [<ffffffff81365a72>] __nfs_fscache_invalidate_page+0x42/0x70 [<ffffffff813553d5>] nfs_invalidate_page+0x75/0x90 [<ffffffff811b8f5e>] truncate_inode_page+0x8e/0x90 [<ffffffff811b90ad>] truncate_inode_pages_range.part.12+0x14d/0x620 [<ffffffff81d6387d>] ? __mutex_lock_slowpath+0x1fd/0x2e0 [<ffffffff811b95d3>] truncate_inode_pages_range+0x53/0x70 [<ffffffff811b969d>] truncate_inode_pages+0x2d/0x40 [<ffffffff811b96ff>] truncate_pagecache+0x4f/0x70 [<ffffffff81356840>] nfs_setattr_update_inode+0xa0/0x120 [<ffffffff81368de4>] nfs3_proc_setattr+0xc4/0xe0 [<ffffffff81357f78>] nfs_setattr+0xc8/0x150 [<ffffffff8122d95b>] notify_change+0x1cb/0x390 [<ffffffff8120a55b>] do_truncate+0x7b/0xc0 [<ffffffff8121f96c>] do_last+0xa4c/0xfd0 [<ffffffff8121ffbc>] path_openat+0xcc/0x670 [<ffffffff81220a0e>] do_filp_open+0x4e/0xb0 [<ffffffff8120ba1f>] do_sys_open+0x13f/0x2b0 [<ffffffff8126aaf6>] compat_SyS_open+0x36/0x50 [<ffffffff81d7204c>] sysenter_dispatch+0x7/0x24 The code at the instruction pointer was disassembled: > (gdb) disas __fscache_uncache_page > Dump of assembler code for function __fscache_uncache_page: > ... > 0xffffffff812a18ff <+31>: mov 0x48(%rbx),%rax > 0xffffffff812a1903 <+35>: cmpb $0x0,0x10(%rax) > 0xffffffff812a1907 <+39>: je 0xffffffff812a19cd <__fscache_uncache_page+237> These instructions make up: ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX); That cmpb is the faulting instruction (%rax is 0). So cookie->def is NULL - which presumably means that the cookie has already been at least partway through __fscache_relinquish_cookie(). What I think may be happening is something like a three-way race on the same file: PROCESS 1 PROCESS 2 PROCESS 3 =============== =============== =============== open(O_TRUNC|O_WRONLY) open(O_RDONLY) open(O_WRONLY) -->nfs_open() -->nfs_fscache_set_inode_cookie() nfs_fscache_inode_lock() nfs_fscache_disable_inode_cookie() __fscache_relinquish_cookie() nfs_inode->fscache = NULL <--nfs_fscache_set_inode_cookie() -->nfs_open() -->nfs_fscache_set_inode_cookie() nfs_fscache_inode_lock() nfs_fscache_enable_inode_cookie() __fscache_acquire_cookie() nfs_inode->fscache = cookie <--nfs_fscache_set_inode_cookie() <--nfs_open() -->nfs_setattr() ... ... -->nfs_invalidate_page() -->__nfs_fscache_invalidate_page() cookie = nfsi->fscache -->nfs_open() -->nfs_fscache_set_inode_cookie() nfs_fscache_inode_lock() nfs_fscache_disable_inode_cookie() -->__fscache_relinquish_cookie() -->__fscache_uncache_page(cookie) <crash> <--__fscache_relinquish_cookie() nfs_inode->fscache = NULL <--nfs_fscache_set_inode_cookie() What is needed is something to prevent process #2 from reacquiring the cookie - and I think checking i_writecount should do the trick. It's also possible to have a two-way race on this if the file is opened O_TRUNC|O_RDONLY instead. Reported-by: Mark Moseley <moseleymark@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com>
229 lines
6.5 KiB
C
229 lines
6.5 KiB
C
/* 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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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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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/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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#ifdef CONFIG_NFS_FSCACHE
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/*
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* set of NFS FS-Cache objects that form a superblock key
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*/
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struct nfs_fscache_key {
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struct rb_node node;
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struct nfs_client *nfs_client; /* the server */
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/* the elements of the unique key - as used by nfs_compare_super() and
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* nfs_compare_mount_options() to distinguish superblocks */
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struct {
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struct {
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unsigned long s_flags; /* various flags
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* (& NFS_MS_MASK) */
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} super;
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struct {
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struct nfs_fsid fsid;
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int flags;
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unsigned int rsize; /* read size */
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unsigned int wsize; /* write size */
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unsigned int acregmin; /* attr cache timeouts */
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unsigned int acregmax;
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unsigned int acdirmin;
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unsigned int acdirmax;
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} nfs_server;
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struct {
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rpc_authflavor_t au_flavor;
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} rpc_auth;
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/* uniquifier - can be used if nfs_server.flags includes
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* NFS_MOUNT_UNSHARED */
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u8 uniq_len;
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char uniquifier[0];
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} key;
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};
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/*
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* fscache-index.c
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*/
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extern struct fscache_netfs nfs_fscache_netfs;
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extern const struct fscache_cookie_def nfs_fscache_server_index_def;
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extern const struct fscache_cookie_def nfs_fscache_super_index_def;
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extern const struct fscache_cookie_def nfs_fscache_inode_object_def;
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extern int nfs_fscache_register(void);
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extern void nfs_fscache_unregister(void);
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/*
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* fscache.c
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*/
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extern void nfs_fscache_get_client_cookie(struct nfs_client *);
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extern void nfs_fscache_release_client_cookie(struct nfs_client *);
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extern void 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_invalidate_page(struct page *, struct inode *);
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extern int nfs_fscache_release_page(struct page *, gfp_t);
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extern int __nfs_readpage_from_fscache(struct nfs_open_context *,
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struct inode *, struct page *);
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extern int __nfs_readpages_from_fscache(struct nfs_open_context *,
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struct inode *, struct address_space *,
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struct list_head *, unsigned *);
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extern void __nfs_readpage_to_fscache(struct inode *, struct page *, int);
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/*
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* wait for a page to complete writing to the cache
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*/
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static inline void nfs_fscache_wait_on_page_write(struct nfs_inode *nfsi,
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struct page *page)
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{
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if (PageFsCache(page))
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fscache_wait_on_page_write(nfsi->fscache, page);
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}
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/*
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* release the caching state associated with a page if undergoing complete page
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* invalidation
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*/
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static inline void nfs_fscache_invalidate_page(struct page *page,
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struct inode *inode)
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{
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if (PageFsCache(page))
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__nfs_fscache_invalidate_page(page, inode);
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}
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/*
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* Retrieve a page from an inode data storage object.
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*/
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static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
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struct inode *inode,
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struct page *page)
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{
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if (NFS_I(inode)->fscache)
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return __nfs_readpage_from_fscache(ctx, inode, page);
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return -ENOBUFS;
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}
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/*
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* Retrieve a set of pages from an inode data storage object.
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*/
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static inline int nfs_readpages_from_fscache(struct nfs_open_context *ctx,
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struct inode *inode,
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struct address_space *mapping,
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struct list_head *pages,
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unsigned *nr_pages)
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{
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if (NFS_I(inode)->fscache)
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return __nfs_readpages_from_fscache(ctx, inode, mapping, pages,
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nr_pages);
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return -ENOBUFS;
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}
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/*
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* Store a page newly fetched from the server in an inode data storage object
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* in the cache.
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*/
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static inline void nfs_readpage_to_fscache(struct inode *inode,
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struct page *page,
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int sync)
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{
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if (PageFsCache(page))
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__nfs_readpage_to_fscache(inode, page, sync);
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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)
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{
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fscache_invalidate(NFS_I(inode)->fscache);
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}
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/*
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* Wait for an object to finish being invalidated.
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*/
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static inline void nfs_fscache_wait_on_invalidate(struct inode *inode)
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{
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fscache_wait_on_invalidate(NFS_I(inode)->fscache);
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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 && (server->options & NFS_OPTION_FSCACHE))
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return "yes";
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return "no ";
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}
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#else /* CONFIG_NFS_FSCACHE */
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static inline int nfs_fscache_register(void) { return 0; }
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static inline void nfs_fscache_unregister(void) {}
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static inline void nfs_fscache_get_client_cookie(struct nfs_client *clp) {}
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static inline void nfs_fscache_release_client_cookie(struct nfs_client *clp) {}
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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 int nfs_fscache_release_page(struct page *page, gfp_t gfp)
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{
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return 1; /* True: may release page */
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}
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static inline void nfs_fscache_invalidate_page(struct page *page,
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struct inode *inode) {}
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static inline void nfs_fscache_wait_on_page_write(struct nfs_inode *nfsi,
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struct page *page) {}
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static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
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struct inode *inode,
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struct page *page)
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{
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return -ENOBUFS;
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}
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static inline int nfs_readpages_from_fscache(struct nfs_open_context *ctx,
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struct inode *inode,
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struct address_space *mapping,
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struct list_head *pages,
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unsigned *nr_pages)
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{
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return -ENOBUFS;
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}
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static inline void nfs_readpage_to_fscache(struct inode *inode,
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struct page *page, int sync) {}
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static inline void nfs_fscache_invalidate(struct inode *inode) {}
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static inline void nfs_fscache_wait_on_invalidate(struct inode *inode) {}
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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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#endif /* CONFIG_NFS_FSCACHE */
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#endif /* _NFS_FSCACHE_H */
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