如何在Linux内核模块中读取/写入文件？ [英] How to read/write files within a Linux kernel module?
问题描述
驱动我坚果 - 你永远不应该在内核。然而，问题是2.6.30不导出
sys_read（）。相反，它包裹在 SYSCALL_DEFINE3 中。所以，如果我在我的模块中使用它，我得到以下警告：$ p $
警告：sys_read[xxx.ko] undefined！
警告：sys_open[xxx.ko] undefined！
显然 insmod 无法加载模块，因为链接 b
$ b
问题：
< 2.6.22之后的内核（其中 sys_read（） / sys_open（）不会被导出）？ b $ b
SYSCALL_DEFINEn（）中的系统调用？你应该知道，你应该尽可能地避免文件I / O。主要思路是深入一层，并调用 VFS级别函数而不是系统调用包括：
#include< linux / fs.h文件>
#include< asm / segment.h>
#include< asm / uaccess.h>
#include< linux / buffer_head.h>
打开一个文件（类似于打开）：
struct file * file_open（const char * path，int flags，int rights）
{
struct file * filp = NULL;
mm_segment_t oldfs;
int err = 0;
oldfs = get_fs（）;
set_fs（get_ds（））;
filp = filp_open（path，flags，rights）;
set_fs（oldfs）; （IS_ERR（filp））{
err = PTR_ERR（filp）;
if
返回NULL;
}
return filp;
$ / code> 关闭一个文件（类似于关闭）：
void file_close（struct file * file）
{
filp_close（file，NULL）;
从文件中读取数据（类似于pread）：
int file_read（struct file * file，unsigned long long offset，unsigned char * data，unsigned int size）
{
mm_segment_t oldfs;
int ret;
oldfs = get_fs（）;
set_fs（get_ds（））;
ret = vfs_read（文件，数据，大小和偏移量）;
set_fs（oldfs）;
return ret;将数据写入文件（类似于pwrite）：
$ b
int file_write（struct file * file，unsigned long long offset，unsigned char * data，unsigned int size）
{
mm_segment_t oldfs;
int ret;
oldfs = get_fs（）;
set_fs（get_ds（））;
ret = vfs_write（文件，数据，大小和偏移）;
set_fs（oldfs）;
return ret;
$ / code>
同步更改文件（类似于fsync）：
int file_sync（结构文件*文件）
{
vfs_fsync（file，0）;
返回0;
原本我建议使用file_fsync，版本。感谢那个可怜的人提出这个改变，但是他的改变被拒绝了。编辑被拒绝之前，我可以检讨它。
I know all the discussions about why one should not read/write files from kernel, instead how to use /proc or netlink to do that. I want to read/write anyway. I have also read
Driving Me Nuts - Things You Never Should Do in the Kernel.
However, problem is 2.6.30 does not export sys_read(). Rather its wrapped in SYSCALL_DEFINE3. So if I use that in my module, I get following warnings:
WARNING: "sys_read" [xxx.ko] undefined!
WARNING: "sys_open" [xxx.ko] undefined!
Obviously insmod cannot load the module because linking does not happen correctly.
Questions:
- How to read/write within kernel after 2.6.22 (where
sys_read()/sys_open() are not exported)?
- In general, how to use system calls wrapped in macro
SYSCALL_DEFINEn() from within the kernel?
解决方案 You should be aware that that you should avoid file I/O when possible. The main idea is to go "one level deeper" and call VFS level functions instead of the syscall handler directly:
Includes:
#include <linux/fs.h>
#include <asm/segment.h>
#include <asm/uaccess.h>
#include <linux/buffer_head.h>
Opening a file (similar to open):
struct file *file_open(const char *path, int flags, int rights)
{
struct file *filp = NULL;
mm_segment_t oldfs;
int err = 0;
oldfs = get_fs();
set_fs(get_ds());
filp = filp_open(path, flags, rights);
set_fs(oldfs);
if (IS_ERR(filp)) {
err = PTR_ERR(filp);
return NULL;
}
return filp;
}
Close a file (similar to close):
void file_close(struct file *file)
{
filp_close(file, NULL);
}
Reading data from a file (similar to pread):
int file_read(struct file *file, unsigned long long offset, unsigned char *data, unsigned int size)
{
mm_segment_t oldfs;
int ret;
oldfs = get_fs();
set_fs(get_ds());
ret = vfs_read(file, data, size, &offset);
set_fs(oldfs);
return ret;
}
Writing data to a file (similar to pwrite):
int file_write(struct file *file, unsigned long long offset, unsigned char *data, unsigned int size)
{
mm_segment_t oldfs;
int ret;
oldfs = get_fs();
set_fs(get_ds());
ret = vfs_write(file, data, size, &offset);
set_fs(oldfs);
return ret;
}
Syncing changes a file (similar to fsync):
int file_sync(struct file *file)
{
vfs_fsync(file, 0);
return 0;
}
[Edit] Originally, I proposed using file_fsync, which is gone in newer kernel versions. Thanks to the poor guy suggesting the change, but whose change was rejected. The edit was rejected before I could review it.
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