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Code Issues Releases Wiki Activity

anonymous inode: move doc to readme

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This commit is contained in:
Ciro Santilli
2018-07-01 16:10:29 +01:00
parent 662d4f25a1
commit 923f655811
6 changed files with 50 additions and 24 deletions
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1
kernel_module/README.adoc
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@@ -19,7 +19,6 @@
... link:dep.c[]
... link:dep2.c[]
. Pseudo filesystems
.. link:anonymous_inode.c[]
.. link:ioctl.c[]
.. link:mmap.c[]
.. link:poll.c[]

21
kernel_module/anonymous_inode.c
View File

@@ -1,20 +1,9 @@
/*
https://stackoverflow.com/questions/4508998/what-is-anonymous-inode
anon_inode_getfd example:
- get an anonymous inode via ioctl from a debugfs entry
- read jiffies from that inode
This method allows getting multiple file descriptors from a single filesystem,
which reduces namespace pollution.
*/
/* https://github.com/cirosantilli/linux-kernel-module-cheat#anonymous-inode */
#include <linux/anon_inodes.h>
#include <linux/debugfs.h>
#include <linux/errno.h> /* EFAULT */
#include <linux/fs.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* min */
#include <linux/module.h>
#include <linux/printk.h> /* printk */
@@ -23,16 +12,18 @@ which reduces namespace pollution.
#include "anonymous_inode.h"
static struct dentry *debugfs_file;
static u32 myval = 1;
static ssize_t read(struct file *filp, char __user *buf, size_t len, loff_t *off)
{
char kbuf[1024];
char kbuf[8];
size_t ret;
ret = snprintf(kbuf, sizeof(kbuf), "%llu", (unsigned long long)jiffies);
ret = snprintf(kbuf, sizeof(kbuf), "%x", myval);
if (copy_to_user(buf, kbuf, ret)) {
ret = -EFAULT;
}
myval <<= 4;
return ret;
}
@@ -47,7 +38,7 @@ static long unlocked_ioctl(struct file *filp, unsigned int cmd, unsigned long ar
switch (cmd) {
case LKMC_ANONYMOUS_INODE_GET_FD:
fd = anon_inode_getfd(
"random",
"todo_what_is_this_for",
&fops_anon,
NULL,
O_RDONLY | O_CLOEXEC

16
kernel_module/user/anonymous_inode.c
View File

@@ -14,10 +14,15 @@ int main(int argc, char **argv)
{
char buf[1024];
int fd_ioctl, fd_ioctl_anon, ret;
size_t i, nreads;
if (argc < 2) {
puts("Usage: ./prog <ioctl-file>");
puts("Usage: ./prog <ioctl-file> [<nreads>]");
return EXIT_FAILURE;
} else if (argc > 2) {
nreads = strtol(argv[2], NULL, 10);
} else {
nreads = 3;
}
fd_ioctl = open(argv[1], O_RDONLY);
if (fd_ioctl == -1) {
@@ -29,11 +34,10 @@ int main(int argc, char **argv)
perror("ioctl");
return EXIT_FAILURE;
}
ret = read(fd_ioctl_anon, buf, sizeof(buf));
printf("%.*s\n", ret, buf);
sleep(1);
ret = read(fd_ioctl_anon, buf, sizeof(buf));
printf("%.*s\n", ret, buf);
for (i = 0; i < nreads; ++i) {
ret = read(fd_ioctl_anon, buf, sizeof(buf));
printf("%.*s\n", ret, buf);
}
close(fd_ioctl_anon);
close(fd_ioctl);
return EXIT_SUCCESS;