ramfs--源码 inode.c

inode.c
 * Resizable simple ram filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *               2000 Transmeta Corp.
 *
 * Usage limits added by David Gibson, Linuxcare Australia.
 * This file is released under the GPL.
 */


/*
 * NOTE! This filesystem is probably most useful
 * not as a real filesystem, but as an example of
 * how virtual filesystems can be written.
 *
 * It doesn't get much simpler than this. Consider
 * that this file implements the full semantics of
 * a POSIX-compliant read-write filesystem.
 *
 * Note in particular how the filesystem does not
 * need to implement any data structures of its own
 * to keep track of the virtual data: using the VFS
 * caches is sufficient.
 */


#include <linux/module.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/ramfs.h>
#include <linux/sched.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <asm/uaccess.h>
#include "internal.h"


#define RAMFS_DEFAULT_MODE 0755


static const struct super_operations ramfs_ops;    /* 针对ramfs的操作回调函数 */
static const struct inode_operations ramfs_dir_inode_operations; /* 针对目录inode的操作回调函数 */ 


 /* 描述底层块设备 */
static struct backing_dev_info ramfs_backing_dev_info = {
.name = "ramfs",
.ra_pages = 0, /* No readahead 由于ramfs直接放在缓存中，所以不需要预读 */ 
       /* 描述底层块设备具备的功能，
           BDI_CAP_NO_ACCT_AND_WRITEBACK含义为不回写脏页、不统计脏页、不自动统计回写的脏页 
           BDI_CAP_MAP_DIRECT 表示块设备支持mmap操作的MAP_PRIVATE
           BDI_CAP_MAP_COPY表示块设备支持mmap操作的MAP_PRIVATE
           BDI_CAP_READ_MAP表示块设备支持mmap操作的PROT_READ
           BDI_CAP_WRITE_MAP表示块设备支持mmap操作的PROT_WRITE
           BDI_CAP_EXEC_MAP表示块设备支持mmap操作的PROT_EXEC
           */
.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK |
 BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
 BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
};


 /* 创建一个inode */
struct inode *ramfs_get_inode(struct super_block *sb, int mode, dev_t dev)
{
        /* 从内存中分配一个inode空间 */
struct inode * inode = new_inode(sb);


if (inode) {
/* 填充inode结构 */
inode->i_mode = mode;                  /* 文件类型 */
inode->i_uid = current_fsuid();       /* 获得当前进程的UID */
inode->i_gid = current_fsgid();       /* 获得当前进程的GID */
inode->i_mapping->a_ops = &ramfs_aops;     /* 注册内存操作回调 */
inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;  /* 保存底层块设备信息 */
mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);   /* 为inode分配内存地址空间 */
mapping_set_unevictable(inode->i_mapping);
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
switch (mode & S_IFMT) {
default:
/* 处理特殊的inode，包括socket、fifo、块设备、字符设备*/
init_special_inode(inode, mode, dev);
break;
case S_IFREG:
/* 普通文件，注册回调函数 */
inode->i_op = &ramfs_file_inode_operations;
inode->i_fop = &ramfs_file_operations;
break;
case S_IFDIR:
/* 目录，注册回调函数 */
inode->i_op = &ramfs_dir_inode_operations;
inode->i_fop = &simple_dir_operations;


/* directory inodes start off with i_nlink == 2 (for "." entry) */
/* 增加文件引用计数即inode->i_nlink，目录的引用计数为2，因为包括了"." 
                        当inode->i_nlink为0时，说明这个inode闲置
*/
inc_nlink(inode);
break;
case S_IFLNK:
inode->i_op = &page_symlink_inode_operations;
break;
}
}
return inode;
}


/*
 * File creation. Allocate an inode, and we're done..
 */
/* SMP-safe */
/* 在指定的目录下创建节点 */
static int
ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
{
       /* 获得一个inode */
struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
int error = -ENOSPC;


if (inode) {
if (dir->i_mode & S_ISGID) {  /* 如果mode带有GID，需要将GID付给inode */
inode->i_gid = dir->i_gid;
if (S_ISDIR(mode))
inode->i_mode |= S_ISGID;
}
d_instantiate(dentry, inode);  /* 用于向dentry结构中填写inode信息 */
dget(dentry); /* Extra count - pin the dentry in core 对dentry->d_count加一*/
error = 0;
dir->i_mtime = dir->i_ctime = CURRENT_TIME;  /* 修改目录的访问时间、inode修改时间 */
}
return error;
}


/* 创建目录 */
static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
{
int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
if (!retval)
inc_nlink(dir);  /* 将目录inode->i_nlink加一 */
return retval;
}


/* 创建文件 */
static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode, struct nameidata *nd)
{
return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
}




/* 建立软连接 */
static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
{
struct inode *inode;
int error = -ENOSPC;


       /* 获得一个inode */
inode = ramfs_get_inode(dir->i_sb, S_IFLNK|S_IRWXUGO, 0);
if (inode) {
int l = strlen(symname)+1;
error = page_symlink(inode, symname, l);  /* 将软连接写入pagecache ，并将页置为脏*/
if (!error) {
if (dir->i_mode & S_ISGID)
inode->i_gid = dir->i_gid;
d_instantiate(dentry, inode);   /* 用于向dentry结构中填写inode信息 */
dget(dentry);    /* dentry->d_count加1 */
dir->i_mtime = dir->i_ctime = CURRENT_TIME;  /* 置操作时间 */
} else
iput(inode);
}
return error;
}




/* 为inode操作注册回调函数 */
static const struct inode_operations ramfs_dir_inode_operations = {
.create = ramfs_create,
.lookup = simple_lookup,
.link = simple_link,
.unlink = simple_unlink,
.symlink = ramfs_symlink,
.mkdir = ramfs_mkdir,
.rmdir = simple_rmdir,
.mknod = ramfs_mknod,
.rename = simple_rename,
};




/* 为超级块操作注册回调 */
static const struct super_operations ramfs_ops = {
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
.show_options = generic_show_options,
};


struct ramfs_mount_opts {
umode_t mode;
};


enum {
Opt_mode,
Opt_err
};


static const match_table_t tokens = {
{Opt_mode, "mode=%o"},
{Opt_err, NULL}
};


struct ramfs_fs_info {
struct ramfs_mount_opts mount_opts;
};


static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
{
substring_t args[MAX_OPT_ARGS];
int option;
int token;
char *p;


opts->mode = RAMFS_DEFAULT_MODE;


while ((p = strsep(&data, ",")) != NULL) {
if (!*p)
continue;


token = match_token(p, tokens, args);
switch (token) {
case Opt_mode:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->mode = option & S_IALLUGO;
break;
/*
* We might like to report bad mount options here;
* but traditionally ramfs has ignored all mount options,
* and as it is used as a !CONFIG_SHMEM simple substitute
* for tmpfs, better continue to ignore other mount options.
*/
}
}


return 0;
}


/* 填充超级块 */
static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
{
struct ramfs_fs_info *fsi;
struct inode *inode = NULL;
struct dentry *root;
int err;


save_mount_options(sb, data);


fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
sb->s_fs_info = fsi;
if (!fsi) {
err = -ENOMEM;
goto fail;
}


err = ramfs_parse_options(data, &fsi->mount_opts);
if (err)
goto fail;


       /* 填充超级块结构体 */
sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = RAMFS_MAGIC;
sb->s_op = &ramfs_ops;  /* 注册超级块操作回调 */
sb->s_time_gran = 1;


       /* 为文件系统root分配inode */
inode = ramfs_get_inode(sb, S_IFDIR | fsi->mount_opts.mode, 0);
if (!inode) {
err = -ENOMEM;
goto fail;
}


      /* 为root分配缓存 */
root = d_alloc_root(inode);
sb->s_root = root;
if (!root) {
err = -ENOMEM;
goto fail;
}


return 0;
fail:  /* 异常处理 */
kfree(fsi);
sb->s_fs_info = NULL;
iput(inode);
return err;
}


/* 装载ramfs的超级块 */
int ramfs_get_sb(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
       /*在内存中分配一个超级块结构 (struct super_block) sb，并初始化其部分成员变量，将成员 s_instances 插入到 rootfs 文件系统类型结构中的 fs_supers 指向的双向链表中。*/
return get_sb_nodev(fs_type, flags, data, ramfs_fill_super, mnt);
}


/* 装载rootfs的超级块 */
static int rootfs_get_sb(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super,
   mnt);
}


/* 卸载超级块 */
static void ramfs_kill_sb(struct super_block *sb)
{
kfree(sb->s_fs_info);
kill_litter_super(sb);
}


static struct file_system_type ramfs_fs_type = {
.name = "ramfs",
.get_sb = ramfs_get_sb,
.kill_sb = ramfs_kill_sb,
};
static struct file_system_type rootfs_fs_type = {
.name = "rootfs",
.get_sb = rootfs_get_sb,
.kill_sb = kill_litter_super,
};




/* 初始化模块，注册文件系统 */
static int __init init_ramfs_fs(void)
{
return register_filesystem(&ramfs_fs_type);
}


/* 退出模块，注销文件系统 */
static void __exit exit_ramfs_fs(void)
{
unregister_filesystem(&ramfs_fs_type);
}


module_init(init_ramfs_fs)
module_exit(exit_ramfs_fs)




/* 初始化rootfs文件系统，在引导开机的过程中调用 */
int __init init_rootfs(void)
{
int err;


      /* 初始化对应的块设备 */
err = bdi_init(&ramfs_backing_dev_info);
if (err)
return err;


       /* 注册rootfs文件系统 */
err = register_filesystem(&rootfs_fs_type);
if (err)
bdi_destroy(&ramfs_backing_dev_info);


return err;
}


MODULE_LICENSE("GPL");