Here is an example tasklet module. The
tasklet_fn
- function runs for a few seconds and in the mean time execution of the
+ function runs for a few seconds. In the meantime, execution of the
example_tasklet_init
- function continues to the exit point.
+ function may continue to the exit point, depending on whether it is interrupted by
+softirq.
1/* @@ -4818,7 +4819,7 @@ better suited to running multiple things in a sequence. 42 43MODULE_DESCRIPTION("Tasklet example"); 44MODULE_LICENSE("GPL");-
So with this example loaded So with this example loaded Although tasklet is easy to use, it comes with several defators, and developers are
+ Although tasklet is easy to use, it comes with several defators, and developers are
discussing about getting rid of tasklet in linux kernel. The tasklet callback
runs in atomic context, inside a software interrupt, meaning that it cannot
sleep or access user-space data, so not all work can be done in a tasklet
handler. Also, the kernel only allows one instance of any given tasklet to be
running at any given time; multiple different tasklet callbacks can run in
parallel.
- In recent kernels, tasklets can be replaced by workqueues, timers, or threaded
+ In recent kernels, tasklets can be replaced by workqueues, timers, or threaded
interrupts.1
While the removal of tasklets remains a longer-term goal, the current kernel contains more
than a hundred uses of tasklets. Now developers are proceeding with the API changes and
the macro
+
To add a task to the scheduler we can use a workqueue. The kernel then uses the
+ To add a task to the scheduler we can use a workqueue. The kernel then uses the
Completely Fair Scheduler (CFS) to execute work within the queue.
+
+
Except for the last chapter, everything we did in the kernel so far we have done as a
+ Except for the last chapter, everything we did in the kernel so far we have done as a
response to a process asking for it, either by dealing with a special file, sending an
There are two types of interaction between the CPU and the rest of the
+ There are two types of interaction between the CPU and the rest of the
computer’s hardware. The first type is when the CPU gives orders to the hardware,
the order is when the hardware needs to tell the CPU something. The second, called
interrupts, is much harder to implement because it has to be dealt with when
convenient for the hardware, not the CPU. Hardware devices typically have a very
small amount of RAM, and if you do not read their information when available, it is
lost.
- Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
+ Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
are two types of IRQ’s, short and long. A short IRQ is one which is expected to take
a very short period of time, during which the rest of the machine will be blocked and
no other interrupts will be handled. A long IRQ is one which can take longer, and
during which other interrupts may occur (but not interrupts from the same
device). If at all possible, it is better to declare an interrupt handler to be
long.
- When the CPU receives an interrupt, it stops whatever it is doing (unless it is
+ When the CPU receives an interrupt, it stops whatever it is doing (unless it is
processing a more important interrupt, in which case it will deal with this one only
when the more important one is done), saves certain parameters on the stack and
calls the interrupt handler. This means that certain things are not allowed in the
@@ -4924,10 +4925,10 @@ heavy work deferred from an interrupt handler. Historically, BH (Linux
naming for Bottom Halves) statistically book-keeps the deferred functions.
Softirq and its higher level abstraction, Tasklet, replace BH since Linux
2.3.
- The way to implement this is to call
+ The way to implement this is to call
In practice IRQ handling can be a bit more complex. Hardware is often
+ In practice IRQ handling can be a bit more complex. Hardware is often
designed in a way that chains two interrupt controllers, so that all the IRQs
from interrupt controller B are cascaded to a certain IRQ from interrupt
controller A. Of course, that requires that the kernel finds out which IRQ it
@@ -4944,7 +4945,7 @@ need to solve another truckload of problems. It is not enough to know if a
certain IRQs has happened, it’s also important to know what CPU(s) it was
for. People still interested in more details, might want to refer to "APIC"
now.
- This function receives the IRQ number, the name of the function,
+ This function receives the IRQ number, the name of the function,
flags, a name for /proc/interrupts and a parameter to be passed to the
interrupt handler. Usually there is a certain number of IRQs available.
How many IRQs there are is hardware-dependent. The flags can include
@@ -4954,16 +4955,16 @@ How many IRQs there are is hardware-dependent. The flags can include
+
Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
+ Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
bunch of GPIO pins. Attaching buttons to those and then having a button press do
something is a classic case in which you might need to use interrupts, so that instead
of having the CPU waste time and battery power polling for a change in input state,
it is better for the input to trigger the CPU to then run a particular handling
function.
- Here is an example where buttons are connected to GPIO numbers 17 and 18 and
+ Here is an example where buttons are connected to GPIO numbers 17 and 18 and
an LED is connected to GPIO 4. You can change those numbers to whatever is
appropriate for your board.
@@ -5112,14 +5113,14 @@ appropriate for your board.
142
143MODULE_LICENSE("GPL");
144MODULE_DESCRIPTION("Handle some GPIO interrupts");
-
+
Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
+ Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
way to do that without rendering the interrupt unavailable for a significant duration
is to combine it with a tasklet. This pushes the bulk of the work off into the
scheduler.
- The example below modifies the previous example to also run an additional task
+ The example below modifies the previous example to also run an additional task
when an interrupt is triggered.
@@ -5293,19 +5294,19 @@ when an interrupt is triggered.
165
166MODULE_LICENSE("GPL");
167MODULE_DESCRIPTION("Interrupt with top and bottom half");
-
+
At the dawn of the internet, everybody trusted everybody completely…but that did
+ At the dawn of the internet, everybody trusted everybody completely…but that did
not work out so well. When this guide was originally written, it was a more innocent
era in which almost nobody actually gave a damn about crypto - least of all kernel
developers. That is certainly no longer the case now. To handle crypto stuff, the
kernel has its own API enabling common methods of encryption, decryption and your
favourite hash functions.
-
+
Calculating and checking the hashes of things is a common operation. Here is a
+ Calculating and checking the hashes of things is a common operation. Here is a
demonstration of how to calculate a sha256 hash within a kernel module.
Install the module:
+ Install the module:
And you should see that the hash was calculated for the test string.
- Finally, remove the test module:
+ And you should see that the hash was calculated for the test string.
+ Finally, remove the test module:
+
Here is an example of symmetrically encrypting a string using the AES algorithm
+ Here is an example of symmetrically encrypting a string using the AES algorithm
and a password.
@@ -5591,10 +5592,10 @@ and a password.
196
197MODULE_DESCRIPTION("Symmetric key encryption example");
198MODULE_LICENSE("GPL");
-
+
The input device driver is a module that provides a way to communicate
+ The input device driver is a module that provides a way to communicate
with the interaction device via the event. For example, the keyboard
can send the press or release event to tell the kernel what we want to
do. The input device driver will allocate a new input structure with
@@ -5602,7 +5603,7 @@ do. The input device driver will allocate a new input structure with
dmesg
+ and sets up input bitfields, device id, version, etc. After that, registers it by calling
dmesg
should show:
@@ -4830,23 +4831,23 @@ Example tasklet starts
Example tasklet init continues...
Example tasklet ends
- DECLARE_TASKLET_OLD
exists for compatibility. For further information, see https://lwn.net/Articles/830964/.
-14.2 Work queues
-15 Interrupt Handlers
-15.1 Interrupt Handlers
- ioctl()
, or issuing a system call. But the job of the kernel is not just to respond to process
requests. Another job, which is every bit as important, is to speak to the hardware
connected to the machine.
- request_irq()
to get your interrupt handler called when the relevant IRQ is received.
- SA_INTERRUPT
to indicate this is a fast interrupt. This function will only succeed if there is not
already a handler on this IRQ, or if you are both willing to share.
-15.2 Detecting button presses
-15.3 Bottom Half
-16 Crypto
-16.1 Hash functions
-1sudo insmod cryptosha256.ko
2sudo dmesg
-1sudo rmmod cryptosha256
-16.2 Symmetric key encryption
-17 Virtual Input Device Driver
- input_register_device()
.
-
Here is an example, vinput, It is an API to allow easy +
Here is an example, vinput, It is an API to allow easy
development of virtual input drivers. The drivers needs to export a
vinput_device()
that contains the virtual device name and
@@ -5618,7 +5619,7 @@ development of virtual input drivers. The drivers needs to export a
read()
Then using Then using
@@ -5627,7 +5628,7 @@ development of virtual input drivers. The drivers needs to export a
This function is passed a This function is passed a
This function will receive a user string to interpret and inject the event using the
+ This function will receive a user string to interpret and inject the event using the
This function is used for debugging and should fill the buffer parameter with the
+ This function is used for debugging and should fill the buffer parameter with the
last event sent in the virtual input device format. The buffer will then be copied to
user.
- vinput devices are created and destroyed using sysfs. And, event injection is done
+ vinput devices are created and destroyed using sysfs. And, event injection is done
through a /dev node. The device name will be used by the userland to export a new
virtual input device.
- The The
In vinput.c, the macro In vinput.c, the macro To create a vinputX sysfs entry and /dev node.
+ To create a vinputX sysfs entry and /dev node.
To unexport the device, just echo its id in unexport:
+ To unexport the device, just echo its id in unexport:
Here the virtual keyboard is one of example to use vinput. It supports all
+ Here the virtual keyboard is one of example to use vinput. It supports all
Simulate a key press on "g" ( Simulate a key press on "g" (
Simulate a key release on "g" ( Simulate a key release on "g" (
+
Up to this point we have seen all kinds of modules doing all kinds of things, but there
+ Up to this point we have seen all kinds of modules doing all kinds of things, but there
was no consistency in their interfaces with the rest of the kernel. To impose some
consistency such that there is at minimum a standardized way to start, suspend and
resume a device a device model was added. An example is shown below, and you can
@@ -6381,13 +6382,13 @@ functions.
97
98MODULE_LICENSE("GPL");
99MODULE_DESCRIPTION("Linux Device Model example");
-
+
+
Sometimes you might want your code to run as quickly as possible,
+ Sometimes you might want your code to run as quickly as possible,
especially if it is handling an interrupt or doing something which might
cause noticeable latency. If your code contains boolean conditions and if
you know that the conditions are almost always likely to evaluate as either
@@ -6406,7 +6407,7 @@ to succeed.
4 bio = NULL;
5 goto out;
6}
- When the When the
+
+
You can not do that. In a kernel module, you can only use kernel functions which are
+ You can not do that. In a kernel module, you can only use kernel functions which are
the functions you can see in /proc/kallsyms.
-
+
You might need to do this for a short time and that is OK, but if you do not enable
+ You might need to do this for a short time and that is OK, but if you do not enable
them afterwards, your system will be stuck and you will have to power it
off.
-
+
For people seriously interested in kernel programming, I recommend kernelnewbies.org
+ For people seriously interested in kernel programming, I recommend kernelnewbies.org
and the Documentation subdirectory within the kernel source code which is not
always easy to understand but can be a starting point for further investigation. Also,
as Linus Torvalds said, the best way to learn the kernel is to read the source code
yourself.
- If you would like to contribute to this guide or notice anything glaringly wrong,
+ If you would like to contribute to this guide or notice anything glaringly wrong,
please create an issue at https://github.com/sysprog21/lkmpg. Your pull requests
will be appreciated.
- Happy hacking!
+ Happy hacking!
1The goal of threaded interrupts is to push more of the work to separate threads, so that the
+ 1The goal of threaded interrupts is to push more of the work to separate threads, so that the
minimum needed for acknowledging an interrupt is reduced, and therefore the time spent handling
the interrupt (where it can’t handle any other interrupts at the same time) is reduced. See
https://lwn.net/Articles/302043/. Here is an example tasklet module. The
So with this example loaded So with this example loaded Although tasklet is easy to use, it comes with several defators, and developers are
+ Although tasklet is easy to use, it comes with several defators, and developers are
discussing about getting rid of tasklet in linux kernel. The tasklet callback
runs in atomic context, inside a software interrupt, meaning that it cannot
sleep or access user-space data, so not all work can be done in a tasklet
handler. Also, the kernel only allows one instance of any given tasklet to be
running at any given time; multiple different tasklet callbacks can run in
parallel.
- In recent kernels, tasklets can be replaced by workqueues, timers, or threaded
+ In recent kernels, tasklets can be replaced by workqueues, timers, or threaded
interrupts.1
While the removal of tasklets remains a longer-term goal, the current kernel contains more
than a hundred uses of tasklets. Now developers are proceeding with the API changes and
the macro
+
To add a task to the scheduler we can use a workqueue. The kernel then uses the
+ To add a task to the scheduler we can use a workqueue. The kernel then uses the
Completely Fair Scheduler (CFS) to execute work within the queue.
+
+
Except for the last chapter, everything we did in the kernel so far we have done as a
+ Except for the last chapter, everything we did in the kernel so far we have done as a
response to a process asking for it, either by dealing with a special file, sending an
There are two types of interaction between the CPU and the rest of the
+ There are two types of interaction between the CPU and the rest of the
computer’s hardware. The first type is when the CPU gives orders to the hardware,
the order is when the hardware needs to tell the CPU something. The second, called
interrupts, is much harder to implement because it has to be dealt with when
convenient for the hardware, not the CPU. Hardware devices typically have a very
small amount of RAM, and if you do not read their information when available, it is
lost.
- Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
+ Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
are two types of IRQ’s, short and long. A short IRQ is one which is expected to take
a very short period of time, during which the rest of the machine will be blocked and
no other interrupts will be handled. A long IRQ is one which can take longer, and
during which other interrupts may occur (but not interrupts from the same
device). If at all possible, it is better to declare an interrupt handler to be
long.
- When the CPU receives an interrupt, it stops whatever it is doing (unless it is
+ When the CPU receives an interrupt, it stops whatever it is doing (unless it is
processing a more important interrupt, in which case it will deal with this one only
when the more important one is done), saves certain parameters on the stack and
calls the interrupt handler. This means that certain things are not allowed in the
@@ -4924,10 +4925,10 @@ heavy work deferred from an interrupt handler. Historically, BH (Linux
naming for Bottom Halves) statistically book-keeps the deferred functions.
Softirq and its higher level abstraction, Tasklet, replace BH since Linux
2.3.
- The way to implement this is to call
+ The way to implement this is to call
In practice IRQ handling can be a bit more complex. Hardware is often
+ In practice IRQ handling can be a bit more complex. Hardware is often
designed in a way that chains two interrupt controllers, so that all the IRQs
from interrupt controller B are cascaded to a certain IRQ from interrupt
controller A. Of course, that requires that the kernel finds out which IRQ it
@@ -4944,7 +4945,7 @@ need to solve another truckload of problems. It is not enough to know if a
certain IRQs has happened, it’s also important to know what CPU(s) it was
for. People still interested in more details, might want to refer to "APIC"
now.
- This function receives the IRQ number, the name of the function,
+ This function receives the IRQ number, the name of the function,
flags, a name for /proc/interrupts and a parameter to be passed to the
interrupt handler. Usually there is a certain number of IRQs available.
How many IRQs there are is hardware-dependent. The flags can include
@@ -4954,16 +4955,16 @@ How many IRQs there are is hardware-dependent. The flags can include
+
Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
+ Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
bunch of GPIO pins. Attaching buttons to those and then having a button press do
something is a classic case in which you might need to use interrupts, so that instead
of having the CPU waste time and battery power polling for a change in input state,
it is better for the input to trigger the CPU to then run a particular handling
function.
- Here is an example where buttons are connected to GPIO numbers 17 and 18 and
+ Here is an example where buttons are connected to GPIO numbers 17 and 18 and
an LED is connected to GPIO 4. You can change those numbers to whatever is
appropriate for your board.
@@ -5112,14 +5113,14 @@ appropriate for your board.
142
143MODULE_LICENSE("GPL");
144MODULE_DESCRIPTION("Handle some GPIO interrupts");
-
+
Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
+ Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
way to do that without rendering the interrupt unavailable for a significant duration
is to combine it with a tasklet. This pushes the bulk of the work off into the
scheduler.
- The example below modifies the previous example to also run an additional task
+ The example below modifies the previous example to also run an additional task
when an interrupt is triggered.
@@ -5293,19 +5294,19 @@ when an interrupt is triggered.
165
166MODULE_LICENSE("GPL");
167MODULE_DESCRIPTION("Interrupt with top and bottom half");
-
+
At the dawn of the internet, everybody trusted everybody completely…but that did
+ At the dawn of the internet, everybody trusted everybody completely…but that did
not work out so well. When this guide was originally written, it was a more innocent
era in which almost nobody actually gave a damn about crypto - least of all kernel
developers. That is certainly no longer the case now. To handle crypto stuff, the
kernel has its own API enabling common methods of encryption, decryption and your
favourite hash functions.
-
+
Calculating and checking the hashes of things is a common operation. Here is a
+ Calculating and checking the hashes of things is a common operation. Here is a
demonstration of how to calculate a sha256 hash within a kernel module.
Install the module:
+ Install the module:
And you should see that the hash was calculated for the test string.
- Finally, remove the test module:
+ And you should see that the hash was calculated for the test string.
+ Finally, remove the test module:
+
Here is an example of symmetrically encrypting a string using the AES algorithm
+ Here is an example of symmetrically encrypting a string using the AES algorithm
and a password.
@@ -5591,10 +5592,10 @@ and a password.
196
197MODULE_DESCRIPTION("Symmetric key encryption example");
198MODULE_LICENSE("GPL");
-
+
The input device driver is a module that provides a way to communicate
+ The input device driver is a module that provides a way to communicate
with the interaction device via the event. For example, the keyboard
can send the press or release event to tell the kernel what we want to
do. The input device driver will allocate a new input structure with
@@ -5602,7 +5603,7 @@ do. The input device driver will allocate a new input structure with
Here is an example, vinput, It is an API to allow easy
+ Here is an example, vinput, It is an API to allow easy
development of virtual input drivers. The drivers needs to export a
Then using Then using
@@ -5627,7 +5628,7 @@ development of virtual input drivers. The drivers needs to export a
This function is passed a This function is passed a
This function will receive a user string to interpret and inject the event using the
+ This function will receive a user string to interpret and inject the event using the
This function is used for debugging and should fill the buffer parameter with the
+ This function is used for debugging and should fill the buffer parameter with the
last event sent in the virtual input device format. The buffer will then be copied to
user.
- vinput devices are created and destroyed using sysfs. And, event injection is done
+ vinput devices are created and destroyed using sysfs. And, event injection is done
through a /dev node. The device name will be used by the userland to export a new
virtual input device.
- The The
In vinput.c, the macro In vinput.c, the macro To create a vinputX sysfs entry and /dev node.
+ To create a vinputX sysfs entry and /dev node.
To unexport the device, just echo its id in unexport:
+ To unexport the device, just echo its id in unexport:
Here the virtual keyboard is one of example to use vinput. It supports all
+ Here the virtual keyboard is one of example to use vinput. It supports all
Simulate a key press on "g" ( Simulate a key press on "g" (
Simulate a key release on "g" ( Simulate a key release on "g" (
+
Up to this point we have seen all kinds of modules doing all kinds of things, but there
+ Up to this point we have seen all kinds of modules doing all kinds of things, but there
was no consistency in their interfaces with the rest of the kernel. To impose some
consistency such that there is at minimum a standardized way to start, suspend and
resume a device a device model was added. An example is shown below, and you can
@@ -6381,13 +6382,13 @@ functions.
97
98MODULE_LICENSE("GPL");
99MODULE_DESCRIPTION("Linux Device Model example");
-
+
+
Sometimes you might want your code to run as quickly as possible,
+ Sometimes you might want your code to run as quickly as possible,
especially if it is handling an interrupt or doing something which might
cause noticeable latency. If your code contains boolean conditions and if
you know that the conditions are almost always likely to evaluate as either
@@ -6406,7 +6407,7 @@ to succeed.
4 bio = NULL;
5 goto out;
6}
- When the When the
+
+
You can not do that. In a kernel module, you can only use kernel functions which are
+ You can not do that. In a kernel module, you can only use kernel functions which are
the functions you can see in /proc/kallsyms.
-
+
You might need to do this for a short time and that is OK, but if you do not enable
+ You might need to do this for a short time and that is OK, but if you do not enable
them afterwards, your system will be stuck and you will have to power it
off.
-
+
For people seriously interested in kernel programming, I recommend kernelnewbies.org
+ For people seriously interested in kernel programming, I recommend kernelnewbies.org
and the Documentation subdirectory within the kernel source code which is not
always easy to understand but can be a starting point for further investigation. Also,
as Linus Torvalds said, the best way to learn the kernel is to read the source code
yourself.
- If you would like to contribute to this guide or notice anything glaringly wrong,
+ If you would like to contribute to this guide or notice anything glaringly wrong,
please create an issue at https://github.com/sysprog21/lkmpg. Your pull requests
will be appreciated.
- Happy hacking!
+ Happy hacking!
1The goal of threaded interrupts is to push more of the work to separate threads, so that the
+ 1The goal of threaded interrupts is to push more of the work to separate threads, so that the
minimum needed for acknowledging an interrupt is reduced, and therefore the time spent handling
the interrupt (where it can’t handle any other interrupts at the same time) is reduced. See
https://lwn.net/Articles/302043/. vinput_register_device()
+ vinput_register_device()
and vinput_unregister_device()
will add a new device to the list of support virtual input devices.
1int init(struct vinput *);
- struct vinput
+ struct vinput
already initialized with an allocated struct input_dev
. The init()
function is responsible for initializing the capabilities of the input device and register
@@ -5635,20 +5636,20 @@ it.
1int send(struct vinput *, char *, int);
- input_report_XXXX
or input_event
call. The string is already copied from user.
1int read(struct vinput *, char *, int);
- class_attribute
+ class_attribute
structure is similar to other attribute types we talked about in section 8:
CLASS_ATTR_WO(export/unexport)
+ CLASS_ATTR_WO(export/unexport)
defined in include/linux/device.h (in this case, device.h is included in include/linux/input.h)
will generate the class_attribute
structures which are named class_attr_export/unexport. Then, put them into
@@ -5669,14 +5670,14 @@ will generate the class_attribute
that should be assigned in vinput_class
. Finally, call class_register(&vinput_class)
to create attributes in sysfs.
-1echo "vkbd" | sudo tee /sys/class/vinput/export
-1echo "0" | sudo tee /sys/class/vinput/unexport
@@ -6137,7 +6138,7 @@ will generate the class_attribute
400
401MODULE_LICENSE("GPL");
402MODULE_DESCRIPTION("Emulate input events");
- KEY_MAX
keycodes. The injection format is the KEY_CODE
such as defined in include/linux/input.h. A positive value means
@@ -6145,12 +6146,12 @@ will generate the class_attribute
while a negative value is a KEY_RELEASE
. The keyboard supports repetition when the key stays pressed for too long. The
following demonstrates how simulation work.
- KEY_G
+ KEY_G
= 34):
1echo "+34" | sudo tee /dev/vinput0
- KEY_G
+ KEY_G
= 34):
18 Standardizing the interfaces: The Device Model
-19 Optimizations
-19.1 Likely and Unlikely conditions
- unlikely
+ unlikely
macro is used, the compiler alters its machine instruction output, so that it
continues along the false branch and only jumps if the condition is true. That
avoids flushing the processor pipeline. The opposite happens if you use the
@@ -6415,34 +6416,34 @@ avoids flushing the processor pipeline. The opposite happens if you use the
-20 Common Pitfalls
-20.1 Using standard libraries
-20.2 Disabling interrupts
-21 Where To Go From Here?
-14.1 Tasklets
tasklet_fn
- function runs for a few seconds and in the mean time execution of the
+ function runs for a few seconds. In the meantime, execution of the
example_tasklet_init
- function continues to the exit point.
+ function may continue to the exit point, depending on whether it is interrupted by
+softirq.
1/*
@@ -4818,7 +4819,7 @@ better suited to running multiple things in a sequence.
42
43MODULE_DESCRIPTION("Tasklet example");
44MODULE_LICENSE("GPL");
- dmesg
+ and sets up input bitfields, device id, version, etc. After that, registers it by calling
dmesg
should show:
@@ -4830,23 +4831,23 @@ Example tasklet starts
Example tasklet init continues...
Example tasklet ends
- DECLARE_TASKLET_OLD
exists for compatibility. For further information, see https://lwn.net/Articles/830964/.
-14.2 Work queues
-15 Interrupt Handlers
-15.1 Interrupt Handlers
- ioctl()
, or issuing a system call. But the job of the kernel is not just to respond to process
requests. Another job, which is every bit as important, is to speak to the hardware
connected to the machine.
- request_irq()
to get your interrupt handler called when the relevant IRQ is received.
- SA_INTERRUPT
to indicate this is a fast interrupt. This function will only succeed if there is not
already a handler on this IRQ, or if you are both willing to share.
-15.2 Detecting button presses
-15.3 Bottom Half
-16 Crypto
-16.1 Hash functions
-1sudo insmod cryptosha256.ko
2sudo dmesg
-1sudo rmmod cryptosha256
-16.2 Symmetric key encryption
-17 Virtual Input Device Driver
- input_register_device()
.
- vinput_device()
that contains the virtual device name and
@@ -5618,7 +5619,7 @@ development of virtual input drivers. The drivers needs to export a
read()
vinput_register_device()
+ vinput_register_device()
and vinput_unregister_device()
will add a new device to the list of support virtual input devices.
1int init(struct vinput *);
- struct vinput
+ struct vinput
already initialized with an allocated struct input_dev
. The init()
function is responsible for initializing the capabilities of the input device and register
@@ -5635,20 +5636,20 @@ it.
1int send(struct vinput *, char *, int);
- input_report_XXXX
or input_event
call. The string is already copied from user.
1int read(struct vinput *, char *, int);
- class_attribute
+ class_attribute
structure is similar to other attribute types we talked about in section 8:
CLASS_ATTR_WO(export/unexport)
+ CLASS_ATTR_WO(export/unexport)
defined in include/linux/device.h (in this case, device.h is included in include/linux/input.h)
will generate the class_attribute
structures which are named class_attr_export/unexport. Then, put them into
@@ -5669,14 +5670,14 @@ will generate the class_attribute
that should be assigned in vinput_class
. Finally, call class_register(&vinput_class)
to create attributes in sysfs.
-1echo "vkbd" | sudo tee /sys/class/vinput/export
-1echo "0" | sudo tee /sys/class/vinput/unexport
@@ -6137,7 +6138,7 @@ will generate the class_attribute
400
401MODULE_LICENSE("GPL");
402MODULE_DESCRIPTION("Emulate input events");
- KEY_MAX
keycodes. The injection format is the KEY_CODE
such as defined in include/linux/input.h. A positive value means
@@ -6145,12 +6146,12 @@ will generate the class_attribute
while a negative value is a KEY_RELEASE
. The keyboard supports repetition when the key stays pressed for too long. The
following demonstrates how simulation work.
- KEY_G
+ KEY_G
= 34):
1echo "+34" | sudo tee /dev/vinput0
- KEY_G
+ KEY_G
= 34):
18 Standardizing the interfaces: The Device Model
-19 Optimizations
-19.1 Likely and Unlikely conditions
- unlikely
+ unlikely
macro is used, the compiler alters its machine instruction output, so that it
continues along the false branch and only jumps if the condition is true. That
avoids flushing the processor pipeline. The opposite happens if you use the
@@ -6415,34 +6416,34 @@ avoids flushing the processor pipeline. The opposite happens if you use the
-20 Common Pitfalls
-20.1 Using standard libraries
-20.2 Disabling interrupts
-21 Where To Go From Here?
-