Linux 文件系統模塊的注冊

用cramfs.ko做的實驗，斷點放在init_cramfs_fs（void）函數的rv = register_filesystem(&cramfs_fs_type);行，執行register_filesystem函數：

register_filesystem (fs=0xda7142e0) at fs/filesystems.c:74

顯示cramfs的file_system_type結構提如下：

{name = 0xda714268 "cramfs", fs_flags = 1,
get_sb = 0xda713150 <cramfs_get_sb>,
kill_sb = 0xc0205bb0 <kill_block_super>, owner = 0xda714320, next = 0x0,
fs_supers = {next = 0x0, prev = 0x0}, s_lock_key = {<No data fields>},
s_umount_key = {<No data fields>}, i_lock_key = {<No data fields>},
i_mutex_key = {<No data fields>}, i_mutex_dir_key = {<No data fields>},
i_alloc_sem_key = {<No data fields>}}

先提一下，實際注冊文件系統的時候是將file_system_type放在以file_systems為表頭的一個鏈表中。

先看下file_systems的內容：

(gdb) p *file_systems
$8 = {name = 0xc06cf3f4 "sysfs", fs_flags = 0,
get_sb = 0xc0259190 <sysfs_get_sb>, kill_sb = 0xc0205c00 <kill_anon_super>,
owner = 0x0, next = 0xc0751460, fs_supers = {next = 0xd78044a0,
prev = 0xd78044a0}, s_lock_key = {<No data fields>},
s_umount_key = {<No data fields>}, i_lock_key = {<No data fields>},
i_mutex_key = {<No data fields>}, i_mutex_dir_key = {<No data fields>},
i_alloc_sem_key = {<No data fields>}}

根據next = 0xc0751460 p *(struct file_system_type *)0xc0751460

{name = 0xc06c0033 "rootfs", fs_flags = 0,
get_sb = 0xc02b7240 <rootfs_get_sb>,
kill_sb = 0xc0205c50 <kill_litter_super>, owner = 0x0, next = 0xc074fc00,
fs_supers = {next = 0xd78046a0, prev = 0xd78046a0},
s_lock_key = {<No data fields>}, s_umount_key = {<No data fields>},
i_lock_key = {<No data fields>}, i_mutex_key = {<No data fields>},
i_mutex_dir_key = {<No data fields>}, i_alloc_sem_key = {<No data fields>}}

rootfs的注冊還在sysfs之後。

register_filesystem函數具體做了什麼？主要是兩點：

1、INIT_LIST_HEAD(&fs->fs_supers);

初始化file_system_type結構體中的fs_supers雙向鏈表，後來會看到它會與該種文件系統類型的super_block結構體的s_instances關聯。

2、find_filesystem(fs->name, strlen(fs->name));

在find_filesystem函數中就是根據name和名字長度遍歷鏈表進行查找的，從而將新的文件系統加到這個鏈表中。

附上一個圖：

文件系統模塊的注冊應該就這麼簡單，注冊完成後，就可以mount並使用該文件系統了。