Use of copy_to_user() and copy_from_user() functions

[anish singh]

On Tue, Feb 12, 2013 at 9:24 AM, Chetan Nanda <chetannanda at gmail.com> wrote:
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> On Mon, Feb 11, 2013 at 5:25 PM, anish singh <anish198519851985 at gmail.com> wrote:
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>> On Mon, Feb 11, 2013 at 4:51 PM, पारस <beparas at gmail.com> wrote:
>> > Hi All,
>> >
>> > To read/write data to user-space from kernel-space we use copy_from_user()
>> > and copy_to_user() functions.
>> >
>> > What is the use of these function?
>> > Why kernel can't directly access user address and read/write on to it?
>> what will happen if the user space process gets scheduled out while
>> you were using it?
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> copy_to/from_user should always be called from process context. So even if a process is scheduled out there is >not impact, as when process schedule back in copying will resume to/from correct page.
because page fault will be triggered and the user space will be swapped in.
 That answers the original question.
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>> > Can any one explain why kernel can't directly access the user-space address.
>> >
>> > Thanks
>> >
>> >
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