What is block device driver in Linux?
A block driver provides access to devices that transfer randomly accessible data in fixed-size blocks—disk drives, primarily. The Linux kernel sees block devices as being fundamentally different from char devices; as a result, block drivers have a distinct interface and their own particular challenges.
What is a block device driver?
Devices that support a file system are known as block devices. Drivers written for these devices are known as block device drivers. Block device drivers can also provide a character driver interface that allows utility programs to bypass the file system and access the device directly. …
What are major and minor numbers in the context of Linux device drivers?
The Linux kernel represents character and block devices as pairs of numbers : . Some major numbers are reserved for particular device drivers. Other major numbers are dynamically assigned to a device driver when Linux boots. Each device name is associated with a minor number.
What is ioctl in Linux drivers?
In computing, ioctl (an abbreviation of input/output control) is a system call for device-specific input/output operations and other operations which cannot be expressed by regular system calls. The ioctl system call first appeared in Version 7 of Unix under that name.
What is a major number in Linux?
The major number is a small integer that serves as the index into a static array of char drivers; Section 3.2. 1 later in this chapter explains how to select a major number. The 2.0 kernel supported 128 devices; 2.2 and 2.4 increased that number to 256 (while reserving the values 0 and 255 for future uses).
Why are block drivers important in Linux kernel?
The Linux kernel sees block devices as being fundamentally different from char devices; as a result, block drivers have a distinct interface and their own particular challenges. Efficient block drivers are critical for performance—and not just for explicit reads and writes in user applications.
How to register a block driver in Linux?
The first step taken by most block drivers is to register themselves with the kernel. The function for this task is register_blkdev (which is declared in ): The arguments are the major number that your device will be using and the associated name (which the kernel will display in /proc/devices ).
How are block devices used in device drivers?
The ioctl Method. Block devices can provide an ioctl method to perform device control functions. The higher-level block subsystem code intercepts a number of ioctl commands before your driver ever gets to see them, however (see drivers/block/ioctl.c in the kernel source for the full set).
What does a USB Request Block ( URB ) do?
Basic concept or ‘What is an URB?’ The basic idea of the new driver is message passing, the message itself is called USB Request Block, or URB for short. An URB consists of all relevant information to execute any USB transaction and deliver the data and status back.