Linux虚拟文件系统在内核初始化的start_kernel()函数中主要调用两个函数来实现。[cpp]view plaincopy print? asmlinkagevoid__initstart_kernel(void) { …… vfs_caches_init_early(); …… vfs_caches_init(totalram_pages); …… }
一、早期初始化
虚拟文件系统的早期初始化有函数vfs_caches_init_early()实现，主要负责dentry和inode的hashtable的初始化工作。
[cpp]view plaincopy print? /*在start_kernel中调用，用于文件系统中早期的初始化*/ void__initvfs_caches_init_early(void) { /*初始化两个hashtable*/ dcache_init_early(); inode_init_early(); }
1.1dcache
[cpp]view plaincopy print? staticvoid__initdcache_init_early(void) { intloop; /*IfhashesaredistributedacrossNUMAnodes,defer *hashallocationuntilvmallocspaceisavailable. */ if(hashdist) return; /*dentryhashtable的空间分配*/ dentry_hashtable= alloc_large_system_hash("Dentrycache", sizeof(structhlist_head), dhash_entries, 13, HASH_EARLY, &d_hash_shift, &d_hash_mask, 0); /*hashtable的各个链表初始化*/ for(loop=0;loop<(1<<d_hash_shift);loop++) INIT_HLIST_HEAD(&dentry_hashtable[loop]); }
1.2inode
[cpp]view plaincopy print? /* *Initializethewaitqueuesandinodehashtable. */ void__initinode_init_early(void) { intloop; /*IfhashesaredistributedacrossNUMAnodes,defer *hashallocationuntilvmallocspaceisavailable. */ if(hashdist) return; /*从cache中分配inodehashtable的内存空间*/ inode_hashtable= alloc_large_system_hash("Inode-cache", sizeof(structhlist_head), ihash_entries, 14, HASH_EARLY, &i_hash_shift, &i_hash_mask, 0); /*初始化hashtable的各个链表*/ for(loop=0;loop<(1<<i_hash_shift);loop++) INIT_HLIST_HEAD(&inode_hashtable[loop]); }
二、后期初始化
这阶段对inode、dentry、mount、字符设备驱动模型以及块设备驱动模型做了相应的初始化。
[cpp]view plaincopy print? /*vfs初始化，在start_kernel中调用*/ void__initvfs_caches_init(unsignedlongmempages) { unsignedlongreserve; /*Basehashsizesonavailablememory,withareserveequalto 150%ofcurrentkernelsize*/ reserve=min((mempages-nr_free_pages())*3/2,mempages-1); mempages-=reserve; /*为路径名申请的cache*/ names_cachep=kmem_cache_create("names_cache",PATH_MAX,0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,NULL); /*dentry及其相关内容初始化*/ dcache_init(); inode_init();/*inode初始化*/ files_init(mempages);/*文件相关信息初始化，包括文件描述符表初始化*/ mnt_init();/*mount的初始化*/ bdev_cache_init(); /*字符设备驱动模型的初始化*/ chrdev_init(); }
2.1dentry初始化
[cpp]view plaincopy print? staticvoid__initdcache_init(void) { intloop; /* *Aconstructorcouldbeaddedforstablestatelikethelists, *butitisprobablynotworthitbecauseofthecachenature *ofthedcache. *//*从cache中申请目录cache*/ dentry_cache=KMEM_CACHE(dentry, SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD); /*注册一个shrinker*/ register_shrinker(&dcache_shrinker); /*Hashmayhavebeensetupindcache_init_early*/ if(!hashdist) return; /*下面的操作在前面的初始化中已经做了*/ dentry_hashtable= alloc_large_system_hash("Dentrycache", sizeof(structhlist_head), dhash_entries, 13, 0, &d_hash_shift, &d_hash_mask, 0); for(loop=0;loop<(1<<d_hash_shift);loop++) INIT_HLIST_HEAD(&dentry_hashtable[loop]); }
2.2 inode初始化
[cpp]view plaincopy print? void__initinode_init(void) { intloop; /*inodeslabcache*/ /*slab中分配inode缓存*/ inode_cachep=kmem_cache_create("inode_cache", sizeof(structinode), 0, (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC| SLAB_MEM_SPREAD), init_once); /*注册icacheshrinker,将参数对应的shrinker加入指定队列*/ register_shrinker(&icache_shrinker); /*Hashmayhavebeensetupininode_init_early*/ if(!hashdist) return; /*分配数组对应空间*/ inode_hashtable= alloc_large_system_hash("Inode-cache", sizeof(structhlist_head), ihash_entries, 14, 0, &i_hash_shift, &i_hash_mask, 0); /*初始化链表组*/ for(loop=0;loop<(1<<i_hash_shift);loop++) INIT_HLIST_HEAD(&inode_hashtable[loop]); }
2.3files初始化
[cpp]view plaincopy print? void__initfiles_init(unsignedlongmempages) { intn; /*申请文件cache*/ filp_cachep=kmem_cache_create("filp",sizeof(structfile),0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,NULL); /* *Onefilewithassociatedinodeanddcacheisveryroughly1K. *Perdefaultdon'tusemorethan10%ofourmemoryforfiles. */ n=(mempages*(PAGE_SIZE/1024))/10; files_stat.max_files=n;/*更新文件统计信息*/ if(files_stat.max_files<NR_FILE) files_stat.max_files=NR_FILE; files_defer_init();/*释放文件描述符表*/ percpu_counter_init(&nr_files,0); }
2.4mount初始化
[cpp]view plaincopy print? void__initmnt_init(void) { unsignedu; interr; init_rwsem(&namespace_sem); /*mntcache初始化*/ mnt_cache=kmem_cache_create("mnt_cache",sizeof(structvfsmount), 0,SLAB_HWCACHE_ALIGN|SLAB_PANIC,NULL); /*mounthashtable内存申请*/ mount_hashtable=(structlist_head*)__get_free_page(GFP_ATOMIC); if(!mount_hashtable) panic("Failedtoallocatemounthashtable\n"); printk("Mount-cachehashtableentries:%lu\n",HASH_SIZE); for(u=0;u<HASH_SIZE;u++) INIT_LIST_HEAD(&mount_hashtable[u]);/*初始化hashtable链表*/ err=sysfs_init();/*sysfs文件系统初始化*/ if(err) printk(KERN_WARNING"%s:sysfs_initerror:%d\n", __func__,err); fs_kobj=kobject_create_and_add("fs",NULL); if(!fs_kobj) printk(KERN_WARNING"%s:kobjcreateerror\n",__func__); init_rootfs();/*初始化ramfs和rootfs*/ init_mount_tree();/*初始化mounttree*/ }[cpp]view plaincopy print? staticvoid__initinit_mount_tree(void) { structvfsmount*mnt; structmnt_namespace*ns; structpathroot; mnt=do_kern_mount("rootfs",0,"rootfs",NULL); if(IS_ERR(mnt)) panic("Can'tcreaterootfs"); ns=create_mnt_ns(mnt);/*为mnt创建命名空间*/ if(IS_ERR(ns)) panic("Can'tallocateinitialnamespace"); /*初始化进程的相关命名空间*/ init_task.nsproxy->mnt_ns=ns; get_mnt_ns(ns);/*命名空间的进程数加一*/ /*更新root的相关字段*/ root.mnt=ns->root; root.dentry=ns->root->mnt_root; /*设置fs的当前路径和当前root*/ set_fs_pwd(current->fs,&root); set_fs_root(current->fs,&root); }
2.4.1创建命名空间
[cpp]view plaincopy print? /** *create_mnt_ns-createsaprivatenamespaceandaddsarootfilesystem *@mnt:pointertothenewrootfilesystemmountpoint */ structmnt_namespace*create_mnt_ns(structvfsmount*mnt) { structmnt_namespace*new_ns; new_ns=alloc_mnt_ns();/*分配命名空间*/ if(!IS_ERR(new_ns)){ /*下面为和mnt建立关系*/ mnt->mnt_ns=new_ns; new_ns->root=mnt; list_add(&new_ns->list,&new_ns->root->mnt_list); } returnnew_ns; }[cpp]view plaincopy print? staticstructmnt_namespace*alloc_mnt_ns(void) { structmnt_namespace*new_ns; /*从cache中分配命名空间*/ new_ns=kmalloc(sizeof(structmnt_namespace),GFP_KERNEL); if(!new_ns) returnERR_PTR(-ENOMEM); /*下面为相关字段的初始化*/ atomic_set(&new_ns->count,1); new_ns->root=NULL; INIT_LIST_HEAD(&new_ns->list); init_waitqueue_head(&new_ns->poll); new_ns->event=0; returnnew_ns; }
2.4.2创建mount
[cpp]view plaincopy print? structvfsmount* do_kern_mount(constchar*fstype,intflags,constchar*name,void*data) { structfile_system_type*type=get_fs_type(fstype); structvfsmount*mnt; if(!type) returnERR_PTR(-ENODEV); mnt=vfs_kern_mount(type,flags,name,data); if(!IS_ERR(mnt)&&(type->fs_flags&FS_HAS_SUBTYPE)&& !mnt->mnt_sb->s_subtype) mnt=fs_set_subtype(mnt,fstype); put_filesystem(type); returnmnt; }[cpp]view plaincopy print? structvfsmount* vfs_kern_mount(structfile_system_type*type,intflags,constchar*name,void*data) { structvfsmount*mnt; char*secdata=NULL; interror; if(!type) returnERR_PTR(-ENODEV); error=-ENOMEM; /*从slab中分配一个mnt*/ mnt=alloc_vfsmnt(name); if(!mnt) gotoout; if(data&&!(type->fs_flags&FS_BINARY_MOUNTDATA)){ secdata=alloc_secdata(); if(!secdata) gotoout_mnt; error=security_sb_copy_data(data,secdata); if(error) gotoout_free_secdata; } /*调用文件系统控制结构体的get_sb()，分配并初始化一个 新的超级块并初始化mnt->mnt_sb字段*/ error=type->get_sb(type,flags,name,data,mnt); if(error<0) gotoout_free_secdata; BUG_ON(!mnt->mnt_sb); error=security_sb_kern_mount(mnt->mnt_sb,flags,secdata); if(error) gotoout_sb; /* *filesystemsshouldneversets_maxbyteslargerthanMAX_LFS_FILESIZE *buts_maxbyteswasanunsignedlonglongformanyreleases.Throw *thiswarningforalittlewhiletotryandcatchfilesystemsthat *violatethisrule.Thiswarningshouldbeeitherremovedor *convertedtoaBUG()in2.6.34. */ WARN((mnt->mnt_sb->s_maxbytes<0),"%ssetsb->s_maxbytesto" "negativevalue(%lld)\n",type->name,mnt->mnt_sb->s_maxbytes); /*初始化mnt相关字段*/ mnt->mnt_mountpoint=mnt->mnt_root; mnt->mnt_parent=mnt; up_write(&mnt->mnt_sb->s_umount); free_secdata(secdata); returnmnt;/*返回mnt*/ out_sb: dput(mnt->mnt_root); deactivate_locked_super(mnt->mnt_sb); out_free_secdata: free_secdata(secdata); out_mnt: free_vfsmnt(mnt); out: returnERR_PTR(error); }
structvfsmount*alloc_vfsmnt(constchar*name) { /*从slab中获得mnt*/ structvfsmount*mnt=kmem_cache_zalloc(mnt_cache,GFP_KERNEL); /*下面进行对mnt的初始化*/ if(mnt){ interr; err=mnt_alloc_id(mnt); if(err) gotoout_free_cache; if(name){ mnt->mnt_devname=kstrdup(name,GFP_KERNEL); if(!mnt->mnt_devname) gotoout_free_id; } atomic_set(&mnt->mnt_count,1); INIT_LIST_HEAD(&mnt->mnt_hash); INIT_LIST_HEAD(&mnt->mnt_child); INIT_LIST_HEAD(&mnt->mnt_mounts); INIT_LIST_HEAD(&mnt->mnt_list); INIT_LIST_HEAD(&mnt->mnt_expire); INIT_LIST_HEAD(&mnt->mnt_share); INIT_LIST_HEAD(&mnt->mnt_slave_list); INIT_LIST_HEAD(&mnt->mnt_slave); #ifdefCONFIG_SMP mnt->mnt_writers=alloc_percpu(int); if(!mnt->mnt_writers) gotoout_free_devname; #else mnt->mnt_writers=0; #endif } returnmnt; #ifdefCONFIG_SMP out_free_devname: kfree(mnt->mnt_devname); #endif out_free_id: mnt_free_id(mnt); out_free_cache: kmem_cache_free(mnt_cache,mnt); returnNULL; }
块设备驱动模型初始化 void__initbdev_cache_init(void) { interr; structvfsmount*bd_mnt; /*blockcache初始化*/ bdev_cachep=kmem_cache_create("bdev_cache",sizeof(structbdev_inode), 0,(SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT| SLAB_MEM_SPREAD|SLAB_PANIC), init_once); /*注册blockdev*/ err=register_filesystem(&bd_type); if(err) panic("Cannotregisterbdevpseudo-fs"); bd_mnt=kern_mount(&bd_type); if(IS_ERR(bd_mnt)) panic("Cannotcreatebdevpseudo-fs"); /* *Thisvfsmountstructureisonlyusedtoobtainthe *blockdev_superblock,sotellkmemleaknottoreportit. */ kmemleak_not_leak(bd_mnt); blockdev_superblock=bd_mnt->mnt_sb;/*Forwriteback*/ } 字符设备驱动模型初始化 void__initchrdev_init(void) { cdev_map=kobj_map_init(base_probe,&chrdevs_lock); /*字符设备驱动初始化*/ bdi_init(&directly_mappable_cdev_bdi); }
虚拟文件系统的初始化工作做了整体的梳理，后面将对涉及到的细节做补充，包括 inode和dentrycacheshrinker的注册、sysfs的初始化等。
