`devb-ram`

Driver for RAM disk interface (QNX Neutrino)

You must be root to start this driver.

Syntax:

devb-ram [cam option[,option]...]
         [disk option[,option]...] 
         [ram option[,option]...]
         [blk option[,option]...] &

Options:

Use commas (,) to separate the options. You can put the cam, disk, ram, and blk groups of options in any order.

`cam` options

quiet: Be quiet: don't display any information on startup.
verbose: Be verbose.

`disk` options

The disk options control the driver's interface to cam-disk.so. If specified, they must follow the disk keyword. For more information, see cam-disk.so.

`ram` options

The ram options control the driver's interface to RAM:

address=addr: The physical address to overlay. The default is not to overlay.
blksize=size: Set the sector size. The default is 512 bytes.
capacity=blocks: Specify the capacity of the RAM drive in the blocks of the size specified by the blksize option. The default is 4096 blocks (2 MB).
nodinit: Don't partition the RAM disk or format a QNX 4 filesystem on it.

`blk` options

The blk options control io-blk.so. These options must follow the blk keyword and must be specified after any general or disk options. For more information, see io-blk.so.

Description:

The devb-ram driver creates a RAM disk interface. When the capacity option isn't specified, devb-ram creates a 2 MB RAM disk.

By default, devb-ram partitions the RAM disk, leaving one block for the partition table itself, and making the remainder of the RAM disk (capacity minus 1) a t77 partition, which it then initializes (internally, not by spawning dinit) to have a blank fs-qnx4.so filesystem on it. If you specify the nodinit option, you can later manually format it, optionally partition the RAM disk with fdisk (but you can make the whole thing a filesystem), and then mount it.

By default, io-blk.so allocates 15% of system RAM for cache. The devb-ram system looks like a disk drive to io-blk.so, so it doesn't know that the cache is unnecessary. You should use the blk cache=... option to reduce the cache size.

Because devb-ram is a block device which reads from and writes to RAM, its operations go through a lot of layers before they actually get to RAM. For a RAM disk with better performance, use the blk ramdisk=... option to io-blk.so. For more information, see “RAM disks” in the Connecting Hardware chapter of the QNX Neutrino User's Guide.

Examples:

Create a 4 MB RAM drive:

devb-ram ram capacity=8192 &

Files:

The devb-ram driver causes io-blk.so to adopt various block special devices under /dev. These devices are normally named hdn, where n is the physical unit number of the device.

This driver could also require the following shared objects:

Binary	Required
`cam-disk.so`	For RAM disk access.
`libcam.so`	Always

Exit status:

The devb-ram driver terminates only if an error occurs during startup, or if it has successfully forked itself upon startup because it hadn't been initially started in the background.

0: The devb-ram driver wasn't started in the background and therefore forked itself. The original process terminated with a zero exit status, the forked process continued.
> 0: An error occurred during startup.

Caveats:

While there's no limit to the size of a disk or partition, I/O (i.e. the lseek(), read() and write() functions) is currently limited to 2 gigabytes per partition (or disk). This I/O limit has no effect on the partition size for mounted filesystems.

Known supported functions include:

chmod(), chown(), close(), closedir(), creat(), devctl(), dup(), dup2(), fcntl(), fpathconf(), fstat(), lseek(), mkdir(), mkfifo(), mknod(), open(), opendir(), pathconf(), read(), readdir(), readlink(), rewinddir(), rmdir(), stat(), symlink(), unlink() (not supported for directories), utime(), write()

Note that certain calls (such as pipe(), as well as read() and write() on FIFOs) may require the pipe manager.

devb-ram