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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LEARN ABOUT SUNOS
kvm_kread
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
The kvm_kread() function transfers data from the kernel address space to the address space of the process. nbytes bytes of data are copied
from the kernel virtual address given by addr to the buffer pointed to by buf.
The kvm_kwrite() function is like kvm_kread(), except that the direction of the transfer is reversed. To use this function, the
kvm_open(3KVM) call that returned kd must have specified write access.
The kvm_uread() function transfers data from the address space of the processes specified in the most recent kvm_getu(3KVM) call. nbytes
bytes of data are copied from the user virtual address given by addr to the buffer pointed to by buf.
The kvm_uwrite() function is like kvm_uread(), except that the direction of the transfer is reversed. To use this function, the
kvm_open(3KVM) call that returned kd must have specified write access. The address is resolved in the address space of the process speci-
fied in the most recent kvm_getu(3KVM) call.
RETURN VALUES
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)