Linux中文件系统注册及mount过程分析4
Linux中文件系统注册及mount过程分析4
先看do_kernel_mount
1079 struct vfsmount *1080 do_kern_mount(const char *fstype, int flags, const char *name, void*data)1081 {1082 struct file_system_type *type = get_fs_type(fstype);1083 struct vfsmount *mnt;1084 if (!type)1085 return ERR_PTR(-ENODEV);1086 mnt = vfs_kern_mount(type, flags, name, data);1087 if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&1088 !mnt->mnt_sb->s_subtype)1089 mnt = fs_set_subtype(mnt, fstype);1090 put_filesystem(type);1091 return mnt;1092 }1093 EXPORT_SYMBOL_GPL(do_kern_mount); |
|---|
这里就用到了最开始说的注册的文件系统，通过get_fs_type来查找是否支持fstype类型的文件系统，例如ext4支持的话就把前面注册的结构返回到这里，以后使用的type都是ext4_fs_type，例如vfs_kern_mount里面传递进去的type，就是ext4_fs_type了，
进入到vfs_kern_mount里面看一下，里面肯定会调到get_sb,
899 struct vfsmount * 900 vfs_kern_mount(struct file_system_type *type, int flags, constchar *name, void *data) 901 { 902 struct vfsmount *mnt; 903 char *secdata = NULL; 904 int error; 905 906 if (!type) 907 return ERR_PTR(-ENODEV); 908 909 error = -ENOMEM; 910 mnt = alloc_vfsmnt(name); 911 if (!mnt) 912 goto out; 913 914 if (flags & MS_KERNMOUNT) 915 mnt->mnt_flags = MNT_INTERNAL; 916 917 if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) { 918 secdata = alloc_secdata(); 919 if (!secdata) 920 goto out_mnt; 921 922 error = security_sb_copy_data(data, secdata); 923 if (error) 924 goto out_free_secdata; 925 } 926*************************在这呢，这里的get_sb就是fs/ext4/super.c里面的ext4_get_sb*********************************** 927 error = type->get_sb(type, flags, name, data, mnt); 928 if (error < 0) 929 goto out_free_secdata; 930 BUG_ON(!mnt->mnt_sb); 931 WARN_ON(!mnt->mnt_sb->s_bdi); 932 mnt->mnt_sb->s_flags |= MS_BORN; 933 934 error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata); 935 if (error) 936 goto out_sb; 937 938 /* 939 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE 940 * but s_maxbytes was an unsigned long long for many releases. Throw 941 * this warning for a little while to try and catch filesystems that 942 * violate this rule. This warning should be either removed or 943 * converted to a BUG() in 2.6.34. 944 */ 945 WARN((mnt->mnt_sb->s_maxbytes < 0), "%s set sb->s_maxbytes to " 946 "negative value (%lld)\n", type->name,mnt->mnt_sb->s_maxbytes); 947 948 mnt->mnt_mountpoint = mnt->mnt_root; 949 mnt->mnt_parent = mnt; 950 up_write(&mnt->mnt_sb->s_umount); 951 free_secdata(secdata); 952 return mnt; 953 out_sb: 954 dput(mnt->mnt_root); 955 deactivate_locked_super(mnt->mnt_sb); 956 out_free_secdata: 957 free_secdata(secdata); 958 out_mnt: 959 free_vfsmnt(mnt); 960 out: 961 return ERR_PTR(error); 962 } 963 964 EXPORT_SYMBOL_GPL(vfs_kern_mount); |
|---|
接下来就要进入到ext4系统里面看一下get_sb做了什么
4232 static int ext4_get_sb(struct file_system_type *fs_type, int flags,4233 const char *dev_name, void *data, struct vfsmount *mnt)4234 {4235 return get_sb_bdev(fs_type, flags, dev_name, data, ext4_fill_super,mnt);4236 } |
|---|
这里面一共调用了两个接口get_sb_bdev和ext4_fill_super，一个文件系统的细节部分都在ext4_fill_super里面去做
get_sb_bdev里面会用到ext4_fill_super，因为要注册一下里面的细节，比如创建节点，文件，目录，链接，读文件，读目录，写文件，写目录，删除文件，很多很多。
后面涉及到了对块设备操作的很多工作，文件系统最关键的就是管理文件，并且是块设备上的，这个块设备就是在get_sb_bdev里面得到的
747 int get_sb_bdev(struct file_system_type *fs_type, 748 int flags, const char *dev_name, void *data, 749 int (*fill_super)(struct super_block *, void *, int), 750 struct vfsmount *mnt) 751 { 752 struct block_device *bdev; 753 struct super_block *s; 754 fmode_t mode = FMODE_READ; 755 int error = 0; 756 757 if (!(flags & MS_RDONLY)) 758 mode |= FMODE_WRITE; 759 760 bdev = open_bdev_exclusive(dev_name, mode, fs_type); 761 if (IS_ERR(bdev)) 762 return PTR_ERR(bdev);…… 799 800 s->s_flags = flags; 801 s->s_mode = mode; 802 strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id)); 803 sb_set_blocksize(s, block_size(bdev)); 804 error = fill_super(s, data, flags & MS_SILENT ? 1 : 0); 805 if (error) { 806 deactivate_locked_super(s); 807 goto error; 808 } 809 810 s->s_flags |= MS_ACTIVE; 811 bdev->bd_super = s; 812 } 813 814 simple_set_mnt(mnt, s); 815 return 0;…… |
|---|
通过这个open_bdev_exclusive拿到设备文件后进入到了error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
就这样，对磁盘文件操作就了解了