Question 1. What Is Mknod And It's Usage ?
mknod is a command which used create the tool report (or) node in Linux file system.
In unix or linux we are able to constitute the whole lot as a document .
Syntax: mknod Name b Major Minor
Name : name of the device document
c : form of tool (ex; char or block tool)
Major : Major wide variety of the device report
Minor : Minor range of the device record
ex : $ mknod /dev/rama c 12 5
MKDEV(int principal, int minor);
Question 2. In How Many Ways We Can Allocate Device Number ?
In 2 ways we will allocate tool numbers
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Question 3. How Can We Allocate Device Number Statically ?
register_chrdev_region() feature will statically allocate tool numbers. Which is said in <linux/fs.H>
int register_chrdev_region(dev_t first, unsigned int rely, char *call);
Return values : In case of success "zero" will return , In case of failure "-1 or poor value " will go back
first is the beginning tool quantity of the range you would love to allocate. The minor number portion of first is regularly zero.
Depend is the full number of contiguous tool numbers you're asking for.
Call is the call of the tool that have to be associated with this variety variety. It will appear in /proc/devices and sysfs.
Question four. How Can We Allocate Device Number Dynamically ?
alloc_chrdev_region()will dynamically allocate tool numbers.
Int alloc_chrdev_region(dev_t *dev, unsigned int firstminor,
unsigned int remember, char *call);
dev is an output-best parameter with a purpose to, on successful of entirety, preserve the primary number on your allocated variety.
Firstminor have to be the requested first minor wide variety to apply; it is also zero
be counted is the full wide variety of contiguous tool numbers you are soliciting for.
Call is the call of the tool that ought to be associated with this variety variety. It'll appear in /proc/gadgets and sysfs.
Question 5. How Can We Free Device Numbers ?
void unregister_chrdev_region(dev_t first, unsigned int matter);
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Question 6. What Is Major Number And It's Usage ?
It's an integer wide variety particularly used to provide the affiliation among the tool motive force and tool report . This number is used by kernel .
The major variety tells you which of them motive force handles which tool report.
Question 7. Can We Have Same Major Number For More Than One Device File ?
yes . We will have .
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Question eight. What Is Minor Number And It's Usage ?
The minor range is used most effective by the driver itself to distinguish which tool it is operating on, simply in case the driving force handles a couple of tool.
one motive force can manage a couple of device .Minor might be used to differentiate the one tool from other devices .
Question nine. What Is Range Of Major And Minor Numbers?
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Question 10. What Is Use Of Dev_t Type ?
This is used to hold device numbers—both the foremost and minor components.
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Question eleven. How To Retrieve Major And Minor Number From Dev_t Type ?
To reap the predominant or minor number of a dev_t, use:
MAJOR(dev_t dev); // to obtain essential wide variety
MINOR(dev_t dev); // to obtain minor variety
int important=MAJOR(dev_t dev);
int minor =MINOR(dev_t dev);
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Question 12. How Can I Use My Own Major And Minor Number For A Device File ?
when you have the primary and minor numbers and need to show them right into a dev_t, use:
register_chrdev_region works properly in case you realize beforehand of time exactly which device numbers you want. Often, however, you will not recognize which primary numbers your device will use; there is a constant effort within the Linux kernel improvement network to transport over to using dynamically-allotted tool numbers.
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Question thirteen. How To See Statically Assigned Major Numbers ?
Some essential tool numbers are statically assigned to the maximum not unusual devices. A list of those devices can be observed in Documentation/gadgets.Txt in the kernel source tree.
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Question 14. What Is The Disadvantage Of Dynamic Device Number Assignment ?
The downside of dynamic project is which you can not create the tool nodes earlier, due to the fact the fundamental variety assigned to your module will vary.
Question 15. Where Can We Write Allocation And Freeing Of Device Number's Code ?
allocation : init feature of a module
freeing : cleanup feature of a module
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