自己的RS232设备作为linux文件系统设备

Question

Is there a way to expose own RS232 AVR device as Linux file system device eg /dev/avr_device ? The program must be written as kernel space module or in user space? Is this possible to do by libfuse ? Maybe should I use FIFO pipes as communication channel with device?

Answer 1

To be able to mount a device, in which you have installed a linux filesystem, you need that device to be a block device , but a serial tty device is a char device , incompatible with that.

To be able to solve that problem in the classical view of the system, you need to develop a block device driver, that attaches to that char device (the serial port) and uses it to control de block device emulation protocol, this means to convert the block number and block data into packets to be sent over the serial line to a receiver at the other side an implement the block device details of being some kind of storage device. This can be done with some effort.... the problem is if using a slow serial line will be of interest to simulate any kind of storage.

The advantage of the last approach is that you only have to simulate a block device and will be able to create any local filesystem available for linux.

On a higher level, you can implement a filesystem type, which is a higher level abstraction (fuse allows you for this) but this makes that a more difficult problem, as you have to implement every filesystem primitives (and believe me, there are far more primitives to emulate a filesystem than a block device) to implement every remote primitive as a set of local primitives (this can be unfeasible for a single programmer only)

This second approach fixes completely the functionality of the filesystem, and fixes completely the set of operations you can do to files to the implemented primitives you write. It is far more difficult and normally lacks uniformity with the rest of the system, so I should not recommend you to follow this approach.

The second approach has only one advantage, and it is: as the filesystem uses high level primitives, these can be encoded more compactly into network messages and be more efficiently transmitted over the line, giving more speed for a slow connection. But at the cost of having to implement all the filesystem functionality, and loosing uniformity on the use of these kind of filesystems (you have to implement user access, security, caching of requests, etc).

In the first approach, you have only to implement 4 or 5 primitives, and you get all the functionality of any filesystem that can be installed on a block device.