MYSQLFS: MySQL FS Char Device

#define CHAR_DEVICE_NAME "fsc_dev"

Character device name, identifies it in /dev/

Definition at line 23 of file fsc_device.h.

#define MAX_BUFFER_LENGTH 5192

Maximum length of each char device buffer. Length defined in MYSQLFS protocol: 300 bytes for command part + 4096 bytes for data part. See protocol.txt for more info.

Definition at line 31 of file fsc_device.h.

Referenced by __fsc_query__(), and fsc_write().

#define QUERY	(	fmt,
		args...		)	printk(KERN_DEBUG "FSC: " fmt, ## args)

Macro for print query

Definition at line 19 of file fsc_device.h.

int __fsc_query__	(	const char *	out_buf,
		const int	out_count,
		char *	in_buf,
		int	in_count
	)

File System Char Device communication channel.

This function writes FS query into output buffer, waits until FS Deamon read it, waits until FS Deamon writes the answer via write function. This function can will block in few situations: 1) the FS sends query but output_buffer is still full (hasn't been read) 2) the FS Char Dev waits until input_buffer contains some data (answer) fsc_query function is always called by kernel filesystem, the return value should be carefully checked and the query should be repeated if error occurs.

Parameters:

	out_buf	Command or data from FS to FS Deamon. Note:
	out_count	Length of out_buf content (number of chars).
	in_buf	Buffer for storing the answer or returning data.
	in_count	Maximum length of the buffer, max number of char that could be written into.

Returns:: FS Deamon response length, number of characters written into input_buffer via write function. -ERESTARTSYS if the char device is currently used or waiting was interrupted by signal -EINVAL if query length is greater then char device output buffer size

Definition at line 298 of file fsc_device.c.

References buffer::data, buffer::deamon_queue, fsc_input_buffer, fsc_output_buffer, fsc_sem, fsc_waitforempty_output(), fsc_waitforfull_input(), buffer::length, MAX_BUFFER_LENGTH, PDEBUG, and result.

Referenced by fsc_query().

void fsc_fini ( void )

FS Character Device fini.

Destroy mutex.

Definition at line 116 of file fsc_device.c.

References query_mutex.

void fsc_init ( void )

FS Character Device initialization.

Initializes wait queues for both input and output buffer, declares buffer contents as empty and initializes semaphore for mutual exclusive access to char device internals.

Definition at line 98 of file fsc_device.c.

References buffer::deamon_queue, fsc_input_buffer, fsc_output_buffer, fsc_sem, buffer::kernel_queue, buffer::length, and query_mutex.

int fsc_open	(	struct inode *	inode,
		struct file *	filp
	)

Open the char device.

Char device is open exclusively, only one open instance in the time.

Parameters:

	inode	Ignored.
	filp	Ignored.

Returns:: Zero on success, -EBUSY if device already open.

Definition at line 159 of file fsc_device.c.

References fsc_available, and PDEBUG.

int fsc_query	(	const char *	out_buf,
		const int	out_count,
		char *	in_buf,
		int	in_count
	)

Wraper for __fsc_query__()

Definition at line 270 of file fsc_device.c.

References __fsc_query__(), query_mutex, and result.

Referenced by query().

ssize_t fsc_read	(	struct file *	filp,
		char *	buf,
		size_t	count,
		loff_t *	f_pos
	)

Char Device read function. Allways called from user space by FS Deamon. The deamon reads content of output_buffer and sends it as commands and data to database. On empty output buffer (zero declared length) the caller will be blocked - added into wait queue. The caller will be woken up after writing any data into output buffer from kernel FS. This function don't support reading larger ammount of data then output buffer size. Greater number of char to be read can be specified, but the maximum ouput buffer length is returned. If count is less than output_buffer length, count characters will be read, but the kernel FS remains blocked until whole output_buffer is read.

Parameters:

	filp	Ignored.
	buf	Buffer for storing output_buffer data.
	count	Number of chars to be read.
	f_pos	Ignored.

Returns:: Number of read characters. - ERESTARTSYS if the char device internals is currently used or waiting was interrupted by signal. -EFAULT if data transfer from kernel to user space failed. -EINVAL if user gives smaller buffer than availible

Definition at line 460 of file fsc_device.c.

References buffer::data, buffer::deamon_queue, fsc_output_buffer, fsc_sem, buffer::kernel_queue, buffer::length, and PDEBUG.

int fsc_read_procmem	(	char *	buf,
		char **	start,
		off_t	offset,
		int	count,
		int *	eof,
		void *	data
	)

Prints information about the fsc device.

Not necessary for running, but useful for checking the char device buffer content. Only way to see what is stored inside the buffers withnout reading or writing into them. Params usually not needed, call "cat /proc/fsc_dev".

Parameters:

	buf	Buffer will contain char device info.
	start	Ignored.
	offset	Ignored.
	count	Ignored.
	eof	End Of File parameter.
	data	Ignored.

Returns:: Number of chars copied to buffer buf.

Definition at line 137 of file fsc_device.c.

References buffer::data, fsc_input_buffer, fsc_output_buffer, and buffer::length.

int fsc_release	(	struct inode *	inode,
		struct file *	filp
	)

Release (close) the char device.

Parameters:

	inode	Ignored.
	filp	Ignored.

Returns:: Zero on success.

Definition at line 180 of file fsc_device.c.

References fsc_available, and PDEBUG.

int fsc_waitforempty_output ( void )

Wait for empty output buffer.

Output buffer is used for storing FS commands and data until FS Deamon reads it. When new attempt from kernel to write into ouput buffer is processed and old data are present, this function blocks current running kernel thread using wait queue. The queue is defined in the output buffer sturcture, kernel always sleeps in the kernel_queue. Caller of this function has to hold the semaphore. After return from waiting with success, the semaphore is set down again.

Returns:: Zero on success (output_buffer.length == 0), -ERESTARTSYS if waitinig was interrupted by the signal, or char device after waiging is used (semaphore is already down)

Definition at line 203 of file fsc_device.c.

References fsc_output_buffer, fsc_sem, buffer::kernel_queue, buffer::length, and PDEBUG.

Referenced by __fsc_query__().

int fsc_waitforfull_input ( void )

Wait for full input buffer.

Input buffer is used for storing response from database or command response written by FS Deamon. When new attempt from kernel to read from input buffer is processed and no data are present, this function blocks current running kernel thread using wait queue. The queue is defined in the input buffer structure, kernel alwazs sleeps in the kernel_queue. Calle of this function has to hold the semaphore. After return from waitin with success, the semaphore is set down again.

Returns:: Zero on success (input_buffer.lenght != 0), -ERESTARTSYS if waiting was interrupted by the signal, or char device after waiging is used (semaphore already down).

Definition at line 241 of file fsc_device.c.

References fsc_input_buffer, fsc_sem, buffer::kernel_queue, buffer::length, and PDEBUG.

Referenced by __fsc_query__().

ssize_t fsc_write	(	struct file *	filp,
		const char *	buf,
		size_t	count,
		loff_t *	f_pos
	)

Char Device write function.

Allways called from user space by FS Deamon. The deamon writes command answers and data from database. On full input_buffer (non-zero declared length) the caller will be blocked - added into wait queue. The caller will be woken up after reading full content of input buffer from kernel FS. This function don't support writing larger ammount of data then input buffer size.

Parameters:

	filp	Ignored.
	buf	Buffer with written data.
	count	Number of chars in the buf buffer.
	f_pos	Ignored.

Returns:: Number of written characters. - ERESTARTSYS if the char device internals is currently used or waiting was interrupted by signal. -EINVAL if count of chars for writting is greater then char device input buffer size. -EFAULT if data transfer from user space to kernel space failed.

Definition at line 385 of file fsc_device.c.

References buffer::data, buffer::deamon_queue, fsc_input_buffer, fsc_sem, buffer::kernel_queue, buffer::length, MAX_BUFFER_LENGTH, and PDEBUG.

module_param	(	fsc_major	,
		int	,
		S_IRUSR
	)

Expose fsc device major number.

atomic_t fsc_available = ATOMIC_INIT(1)

Atomic variable for determinig usage of fsc device by exactly one user at the moment.

Definition at line 53 of file fsc_device.c.

Referenced by fsc_open(), and fsc_release().

struct file_operations fsc_fops

This kernel structure contains informations about operations supported by fsc device.

Definition at line 82 of file fsc_device.c.

struct file_operations fsc_fops

Initial value:

 {
  .read = fsc_read,        
  .write = fsc_write,      
  .open = fsc_open,        
  .release = fsc_release   
}

This kernel structure contains informations about operations supported by fsc device.

Definition at line 82 of file fsc_device.c.

struct buffer fsc_input_buffer

Input buffer stores data to be written to char device by the deamon.

Definition at line 49 of file fsc_device.c.

Referenced by __fsc_query__(), fsc_init(), fsc_read_procmem(), fsc_waitforfull_input(), and fsc_write().

int fsc_major

FSC Device module major number.

Definition at line 65 of file fsc_device.c.

int fsc_major = 0

FSC Device module major number.

Definition at line 65 of file fsc_device.c.

struct buffer fsc_output_buffer

Output buffer stores data to be read from char device by the deamon.

Definition at line 45 of file fsc_device.c.

Referenced by __fsc_query__(), fsc_init(), fsc_read(), fsc_read_procmem(), and fsc_waitforempty_output().

struct semaphore fsc_sem

Semaphore for mutual exclusive access to fsc device buffers.

Definition at line 57 of file fsc_device.c.

Referenced by __fsc_query__(), fsc_init(), fsc_read(), fsc_waitforempty_output(), fsc_waitforfull_input(), and fsc_write().

struct mutex query_mutex

Structure for mutex

Definition at line 61 of file fsc_device.c.

Referenced by fsc_fini(), fsc_init(), and fsc_query().

MySQL FS Char Device
[MySQL FS Kernel Module]

Classes

Defines

Functions

Variables

Define Documentation

Function Documentation

Variable Documentation


Classes
struct	buffer
Defines
#define	QUERY(fmt, args...) printk(KERN_DEBUG "FSC: " fmt, ## args)
#define	CHAR_DEVICE_NAME "fsc_dev"
#define	MAX_BUFFER_LENGTH 5192
Functions
	module_param (fsc_major, int, S_IRUSR)
ssize_t	fsc_read (struct file filp, char buf, size_t count, loff_t *f_pos)
	Char Device read function. Allways called from user space by FS Deamon. The deamon reads content of output_buffer and sends it as commands and data to database. On empty output buffer (zero declared length) the caller will be blocked - added into wait queue. The caller will be woken up after writing any data into output buffer from kernel FS. This function don't support reading larger ammount of data then output buffer size. Greater number of char to be read can be specified, but the maximum ouput buffer length is returned. If count is less than output_buffer length, count characters will be read, but the kernel FS remains blocked until whole output_buffer is read.
ssize_t	fsc_write (struct file filp, const char buf, size_t count, loff_t *f_pos)
	Char Device write function.
int	fsc_release (struct inode inode, struct file filp)
	Release (close) the char device.
int	fsc_open (struct inode inode, struct file filp)
	Open the char device.
void	fsc_init (void)
	FS Character Device initialization.
void	fsc_fini (void)
	FS Character Device fini.
int	fsc_read_procmem (char buf, char start, off_t offset, int count, int eof, void *data)
	Prints information about the fsc device.
int	fsc_waitforempty_output (void)
	Wait for empty output buffer.
int	fsc_waitforfull_input (void)
	Wait for full input buffer.
int	__fsc_query__ (const char out_buf, const int out_count, char in_buf, int in_count)
	File System Char Device communication channel.
int	fsc_query (const char out_buf, const int out_count, char in_buf, int in_count)
Variables
buffer	fsc_output_buffer
buffer	fsc_input_buffer
atomic_t	fsc_available = ATOMIC_INIT(1)
semaphore	fsc_sem
mutex	query_mutex
int	fsc_major = 0
file_operations	fsc_fops
int	fsc_major
file_operations	fsc_fops

MySQL FS Char Device [MySQL FS Kernel Module]

Classes

Defines

Functions

Variables

Define Documentation

Function Documentation

Variable Documentation

MySQL FS Char Device
[MySQL FS Kernel Module]