fedora core 6 1.2949 + vserver 2.2.0

[linux-2.6.git] / include / linux / uaccess.h

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 391e7ed..975c963 100644 (file)
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -1,8 +1,43 @@
 #ifndef __LINUX_UACCESS_H__
 #define __LINUX_UACCESS_H__
 
+#include <linux/preempt.h>
 #include <asm/uaccess.h>
 
+/*
+ * These routines enable/disable the pagefault handler in that
+ * it will not take any locks and go straight to the fixup table.
+ *
+ * They have great resemblance to the preempt_disable/enable calls
+ * and in fact they are identical; this is because currently there is
+ * no other way to make the pagefault handlers do this. So we do
+ * disable preemption but we don't necessarily care about that.
+ */
+static inline void pagefault_disable(void)
+{
+       inc_preempt_count();
+       /*
+        * make sure to have issued the store before a pagefault
+        * can hit.
+        */
+       barrier();
+}
+
+static inline void pagefault_enable(void)
+{
+       /*
+        * make sure to issue those last loads/stores before enabling
+        * the pagefault handler again.
+        */
+       barrier();
+       dec_preempt_count();
+       /*
+        * make sure we do..
+        */
+       barrier();
+       preempt_check_resched();
+}
+
 #ifndef ARCH_HAS_NOCACHE_UACCESS
 
 static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
@@ -19,4 +54,34 @@ static inline unsigned long __copy_from_user_nocache(void *to,
 
 #endif         /* ARCH_HAS_NOCACHE_UACCESS */
 
+/**
+ * probe_kernel_address(): safely attempt to read from a location
+ * @addr: address to read from - its type is type typeof(retval)*
+ * @retval: read into this variable
+ *
+ * Safely read from address @addr into variable @revtal.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ * We ensure that the __get_user() is executed in atomic context so that
+ * do_page_fault() doesn't attempt to take mmap_sem.  This makes
+ * probe_kernel_address() suitable for use within regions where the caller
+ * already holds mmap_sem, or other locks which nest inside mmap_sem.
+ * This must be a macro because __get_user() needs to know the types of the
+ * args.
+ *
+ * We don't include enough header files to be able to do the set_fs().  We
+ * require that the probe_kernel_address() caller will do that.
+ */
+#define probe_kernel_address(addr, retval)             \
+       ({                                              \
+               long ret;                               \
+               mm_segment_t old_fs = get_fs();         \
+                                                       \
+               set_fs(KERNEL_DS);                      \
+               pagefault_disable();                    \
+               ret = __get_user(retval, (__force typeof(retval) __user *)(addr));              \
+               pagefault_enable();                     \
+               set_fs(old_fs);                         \
+               ret;                                    \
+       })
+
 #endif         /* __LINUX_UACCESS_H__ */