CODEWITHSUNDEEP
linuxkernel
injoy
injoy

Reputation: 4373

Why does the kernel use the copy_to_user() function?

Why does the kernel use the copy_to_user function?

Couldn't it just directly operate on data in the user space?

Upvotes: 0

Views: 1531

Answers (2)

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

kernel and user-space applications have different address spaces, so copying to user space require an address space change. Each process has its own (user) address space.

Also, kernel should never crash when copying to user space, so the copy_to_user function probably checks that the destination address is valid (perhaps that address should be paged-in, e.g. from swap space).

Read more about linux kernel, syscalls, processes, address space ...

Upvotes: 4

DigitalRoss
DigitalRoss

Reputation: 146053

If a given kernel were written for only one architecture this may or may not be a reasonable choice.

There are a lot of considerations that may vary per architecture and therefore require some sort of polymorphic operation...

  • protection ... the kernel may have too many or too few access rights, either way may require extra code on a given target

  • address space ... the user space and kernel space may overlap, and so a target-specific solution or temporary map would be needed

  • page fault management ... access to the user space can fault and this needs to be either avoided or allowed. Confining the access to a given specific place allows either extra setup or identification of the reason for the fault.

Upvotes: 4

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