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Old 09-20-2016, 09:08 AM   #1
vlrk
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Registered: Dec 2008
Posts: 39

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using mknod to create a device file.


Hi All,

Here i am using below sample code to create a character device file.
mknod returns success but when i do ls -ltr at "/home/xxxx/" i donot see any file there with temp_dev.

Any thing i am missing here to understand?.

Code:
 1#include <stdio.h>
 2#include <sys/types.h>
 3#include <sys/stat.h>
 4#include <fcntl.h>
 5#include <unistd.h>
 6#include <string.h>
 7#include <error.h>
 8
 9int main()
10{
11    dev_t dev;
12    int status;
13    int errno;
14
15    if (status = mknod("/home/xxxx/temp_dev",S_IRUSR|S_IWUSR|S_IFCHR, dev))
16    {
17        printf("%s \n", strerror(errno));
18        sleep(30);
19    }
20    return 0;
21}
 
Old 09-20-2016, 06:23 PM   #2
jpollard
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It isn't going to work.

The mknod uses the contents of dev to determine how to create the file. Very likely, the contents of dev are 0, which isn't used.

The mknod system call is really not used to create devices in linux. The /dev/xxxx entries are created when a driver is loaded, and the driver registers with the kernel to allocate a device/unit value, which is only presented for legacy use - the kernel itself doesn't use them anymore as the directory entry in /dev (a devtmpfs filesystem) directly connects to the driver internal structures for access.

Linux also doesn't really distinguish a difference between block and character devices, though for historical compatibility, the bits are still set.

One of the other things is that only root could create a device. The only non-root devices allowed are sockets (not created via mknod) and fifo files (you don't use mknod to create those - you use mkfifo (a library function, not system call).
 
Old 09-21-2016, 03:42 AM   #3
vlrk
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Thanks Pollard for the info.
 
  


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