February 1998
Intermediate to advanced
439 pages
13h 46m
English
Content preview from Linux Device DriversBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
The ioctl Method
Like char devices, block devices can be acted on by using the ioctl system call. The only relevant difference between the two implementations is that block drivers share a number of common ioctl commands that most drivers are expected to support.
The commands that block drivers usually handle are
the following, declared in <linux/fs.h>:
-
BLKGETSIZE Retrieve the size of the current device, expressed as the number of sectors. The value of
argpassed by the system call is a pointer to alongvalue and should be used to copy the size to a user-space variable. This ioctl command is used, for instance, by mkfs to know the size of the filesystem being created.-
BLKFLSBUF Literally, ``flush buffers.'' The implementation of this command is the same for every device and is shown later with the sample code for the whole ioctl method.
-
BLKRAGET Used to get the current read-ahead value for the device. The current value should be written to user space as a
longitem using the pointer passed to ioctl inarg.-
BLKRASET Set the read-ahead value. The user process passes the new value in
arg.-
BLKRRPART Reread the partition table. This command is meaningful only for partitionable devices, introduced later in Section 12.7.
-
BLKROSET,BLKROGET These commands are used to change and check the read-only flag for the device. They are implemented by the macro
RO_IOCTLS(kdev_t dev, unsigned long where)because the code is device-independent. The macro is defined inblk.h.
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.