Drive Debug Print to proc virtual file 1

PRINTK will put the data in the kernel's 1 buffers, the other way to output information from the hardware, when we want to view the previous information can be used DMESG command to print out the information in the buffer. The DMESG command prints out the information from/proc/kmsg

Proc is a virtual file system

When the system starts,

There's mount-a in there. A means that all the file systems are hooked up.

All file systems in the file fstab, such as the proc file system mounted in the/proc directory

To view mounted file systems

The files inside the virtual file system proc are generated by the kernel, and the properties are read

You can use Cat/proc/kmsg to view kernel output information, and there will be a print level in front of each line of information

The use of cat/proc/kmsg there is no output information, it may be the problem of the read and write mechanism inside

Drivers inside are used PRINTK, assuming that the kernel printing information is very much, the driver to print the information separately to exist somewhere, do not want to be mixed with other things, you can imitate the construction of/proc/kmsg file, driver information printing to another buffer inside

PRINTK information in two ways, all the way there log_buf inside (can be read through/proc/kmsg, through the DMESG command to read the/proc/kmsg file), printed out. In the following: Define 1 buf such as mulog_buf, generate 1 files/proc/mymsg, read the file/proc/mymsg Bar information print out, drive MYPRINTK the information exists LOG_BUF

In the kernel of the FS directory under the proc, there are proc of various operating functions

Analyzing the PROC_MISC.C entry function

If the Config_printk,create_proc_entry function is configured to create 1 entries in the proc directory, the 1th parameter name is kmsg, the 2nd parameter is the attribute (read-only), and the 3rd parameter is the parent, which represents the proc root directory. The file_operation structure of this entry after it is created. When the application opens/proc/kmsg, Open,read,write uses the structure proc_kmsg_operation (file_operation) open,read,write

Search for other programs to call the Create_proc_entry function to see what files are included.

Ring Buffer

buf Array

printk.c inside

The head is the same as the tail (read and write position ) is empty, when there is data, the end of the unequal will wake up

The data is read from the ring buffer after wake, and then returned to the user by calling _put_user