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Top Forums Programming What is use of "char __user *buf"? Post 302837267 by shamrock on Thursday 25th of July 2013 12:29:37 PM
Old 07-25-2013
The use of char __user *buf is typically found in the linux kernel...denoting that this address is in the user space. For example when writing to disk the kernel copies the contents of *buf into a kernel space buffer before writing it out to disk. Similarly when a process requests a read operation...the device driver at the behest of the kernel reads the desired disk blocks into a kernel space buffer...and then copies them into the user space buffer pointed to by *buf.
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kvm_kread(3KVM) 					    Kernel VM Library Functions 					   kvm_kread(3KVM)

NAME
kvm_kread, kvm_kwrite, kvm_uread, kvm_uwrite - copy data to or from a kernel image or running system SYNOPSIS
cc [ flag... ] file... -lkvm [ library...] #include <kvm.h> ssize_t kvm_kread(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes); ssize_t kvm_kwrite(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes); ssize_t kvm_uread(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes); ssize_t kvm_uwrite(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes); DESCRIPTION
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On success, these functions return the number of bytes actually transferred. On failure, they return -1. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Stable | +-----------------------------+-----------------------------+ |MT-Level |Unsafe | +-----------------------------+-----------------------------+ SEE ALSO
kvm_getu(3KVM), kvm_nlist(3KVM), kvm_open(3KVM), attributes(5) SunOS 5.10 2 May 2002 kvm_kread(3KVM)
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