[PATCH] uml: Adds /proc/sysemu to toggle SYSEMU usage.

Adds /proc/sysemu to toggle SYSEMU usage.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/kernel/process.c

@@ -246,7 +246,7 @@ void __init check_ptrace(void)
 	printk("OK\n");
 
 	printk("Checking syscall emulation patch for ptrace...");
-	use_sysemu = 0;
+	set_using_sysemu(0);
 	pid = start_ptraced_child(&stack);
 	if(ptrace(PTRACE_SYSEMU, pid, 0, 0) >= 0) {
 		struct user_regs_struct regs;
@@ -269,7 +269,7 @@ void __init check_ptrace(void)
 
 		if (!force_sysemu_disabled) {
 			printk("found\n");
-			use_sysemu = 1;
+			set_using_sysemu(1);
 		} else {
 			printk("found but disabled\n");
 		}

arch/um/kernel/skas/include/ptrace-skas.h

@@ -15,7 +15,9 @@
 #ifndef PTRACE_SYSEMU
 #define PTRACE_SYSEMU 31
 #endif
-extern int use_sysemu;
+
+void set_using_sysemu(int value);
+int get_using_sysemu(void);
 
 #include "skas_ptregs.h"
 

arch/um/kernel/skas/process.c

@@ -28,10 +28,6 @@
 #include "chan_user.h"
 #include "signal_user.h"
 
-#ifdef PTRACE_SYSEMU
-int use_sysemu = 0;
-#endif
-
 int is_skas_winch(int pid, int fd, void *data)
 {
 	if(pid != getpid())
@@ -61,7 +57,8 @@ static void handle_segv(int pid)
 	segv(fault.addr, 0, FAULT_WRITE(fault.is_write), 1, NULL);
 }
 
-static void handle_trap(int pid, union uml_pt_regs *regs)
+/*To use the same value of using_sysemu as the caller, ask it that value (in local_using_sysemu)*/
+static void handle_trap(int pid, union uml_pt_regs *regs, int local_using_sysemu)
 {
 	int err, syscall_nr, status;
 
@@ -72,10 +69,8 @@ static void handle_trap(int pid, union uml_pt_regs *regs)
 		return;
 	}
 
-#ifdef PTRACE_SYSEMU
-	if (!use_sysemu)
+	if (!local_using_sysemu)
 	{
-#endif
 		err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET, __NR_getpid);
 		if(err < 0)
 			panic("handle_trap - nullifying syscall failed errno = %d\n",
@@ -90,9 +85,7 @@ static void handle_trap(int pid, union uml_pt_regs *regs)
 		if((err < 0) || !WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
 			panic("handle_trap - failed to wait at end of syscall, "
 			      "errno = %d, status = %d\n", errno, status);
-#ifdef PTRACE_SYSEMU
 	}
-#endif
 
 	handle_syscall(regs);
 }
@@ -147,14 +140,15 @@ void start_userspace(int cpu)
 void userspace(union uml_pt_regs *regs)
 {
 	int err, status, op, pid = userspace_pid[0];
+	int local_using_sysemu; /*To prevent races if using_sysemu changes under us.*/
 
 	restore_registers(regs);
 		
-#ifdef PTRACE_SYSEMU
-	if (use_sysemu)
+	local_using_sysemu = get_using_sysemu();
+
+	if (local_using_sysemu)
 		err = ptrace(PTRACE_SYSEMU, pid, 0, 0);
 	else
-#endif
 		err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
 	if(err)
 		panic("userspace - PTRACE_SYSCALL failed, errno = %d\n", 
@@ -174,7 +168,7 @@ void userspace(union uml_pt_regs *regs)
 				handle_segv(pid);
 				break;
 			case SIGTRAP:
-			        handle_trap(pid, regs);
+			        handle_trap(pid, regs, local_using_sysemu);
 				break;
 			case SIGIO:
 			case SIGVTALRM:
@@ -193,14 +187,16 @@ void userspace(union uml_pt_regs *regs)
 
 		restore_registers(regs);
 
-#ifdef PTRACE_SYSEMU
-		if (use_sysemu)
+		/*Now we ended the syscall, so re-read local_using_sysemu.*/
+		local_using_sysemu = get_using_sysemu();
+
+		if (local_using_sysemu)
 			op = singlestepping_skas() ? PTRACE_SINGLESTEP :
 				PTRACE_SYSEMU;
 		else
-#endif
 			op = singlestepping_skas() ? PTRACE_SINGLESTEP :
 				PTRACE_SYSCALL;
+
 		err = ptrace(op, pid, 0, 0);
 		if(err)
 			panic("userspace - PTRACE_SYSCALL failed, "

arch/um/kernel/skas/process_kern.c

@@ -6,6 +6,12 @@
 #include "linux/sched.h"
 #include "linux/slab.h"
 #include "linux/ptrace.h"
+#include "linux/proc_fs.h"
+#include "linux/file.h"
+#include "linux/errno.h"
+#include "linux/init.h"
+#include "asm/uaccess.h"
+#include "asm/atomic.h"
 #include "kern_util.h"
 #include "time_user.h"
 #include "signal_user.h"
@@ -17,6 +23,59 @@
 #include "kern.h"
 #include "mode.h"
 
+#ifdef PTRACE_SYSEMU
+static atomic_t using_sysemu;
+#endif
+
+void set_using_sysemu(int value)
+{
+	atomic_set(&using_sysemu, value);
+}
+
+int get_using_sysemu(void)
+{
+	return atomic_read(&using_sysemu);
+}
+
+int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
+{
+	if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size) /*No overflow*/
+		*eof = 1;
+
+	return strlen(buf);
+}
+
+int proc_write_sysemu(struct file *file,const char *buf, unsigned long count,void *data)
+{
+	char tmp[2];
+
+	if (copy_from_user(tmp, buf, 1))
+		return -EFAULT;
+
+	if (tmp[0] == '0' || tmp[0] == '1')
+		set_using_sysemu(tmp[0] - '0');
+	return count; /*We use the first char, but pretend to write everything*/
+}
+
+int __init make_proc_sysemu(void)
+{
+	struct proc_dir_entry *ent;
+
+	ent = create_proc_entry("sysemu", 00600, &proc_root);
+	ent->read_proc  = proc_read_sysemu;
+	ent->write_proc = proc_write_sysemu;
+
+	if (ent == NULL)
+	{
+		printk("Failed to register /proc/sysemu\n");
+		return(0);
+	}
+
+	return 0;
+}
+
+late_initcall(make_proc_sysemu);
+
 int singlestepping_skas(void)
 {
 	int ret = current->ptrace & PT_DTRACE;