MFp4 (111746+):

  Redo the checking for 2.6 emulation. We now cache the value of
  use26 and replace calls to linux_get_osrelease() + parsing with
  a call to linux_use26(). Typical path is lockless now.

  Pointed out by: kib

This allows to ship RELENG_7_0 with a default osrelease of 2.4.2 and the
possibility to enable 2.6.x emulation without the possible performance
impact of the previous version of the check.

Submitted by:	rdivacky

3 files changed, 33 insertions, 9 deletions

diff --git a/sys/compat/linux/linux_mib.c b/sys/compat/linux/linux_mib.c
index 0721d529bea0..3b025114371f 100644
--- a/sys/compat/linux/linux_mib.c
+++ b/sys/compat/linux/linux_mib.c
@@ -52,6 +52,7 @@ struct linux_prison {
 	char	pr_osname[LINUX_MAX_UTSNAME];
 	char	pr_osrelease[LINUX_MAX_UTSNAME];
 	int	pr_oss_version;
+	int	pr_use_linux26;	/* flag to determine whether to use 2.6 emulation */
 };
 
 SYSCTL_NODE(_compat, OID_AUTO, linux, CTLFLAG_RW, 0,
@@ -82,6 +83,7 @@ SYSCTL_PROC(_compat_linux, OID_AUTO, osname,
 	    "Linux kernel OS name");
 
 static char	linux_osrelease[LINUX_MAX_UTSNAME] = "2.4.2";
+static int	linux_use_linux26 = 0;
 
 static int
 linux_sysctl_osrelease(SYSCTL_HANDLER_ARGS)
@@ -227,19 +229,45 @@ linux_get_osrelease(struct thread *td, char *dst)
 }
 
 int
+linux_use26(struct thread *td)
+{
+	struct prison *pr;
+	struct linux_prison *lpr;
+	int use26 = 0;		/* defaults to off */
+
+	pr = td->td_ucred->cr_prison;
+	if (pr != NULL) {
+		mtx_lock(&pr->pr_mtx);
+		if (pr->pr_linux != NULL) {
+			lpr = (struct linux_prison *)pr->pr_linux;
+			use26 = lpr->pr_use_linux26;
+		}
+		mtx_unlock(&pr->pr_mtx);
+	} else
+		use26 = linux_use_linux26;
+	
+	return (use26);
+}
+
+int
 linux_set_osrelease(struct thread *td, char *osrelease)
 {
 	struct prison *pr;
 	struct linux_prison *lpr;
+	int use26;
+
+	use26 = (strlen(osrelease) >= 3 && osrelease[2] == '6');
 
 	pr = linux_get_prison(td);
 	if (pr != NULL) {
 		lpr = (struct linux_prison *)pr->pr_linux;
 		strcpy(lpr->pr_osrelease, osrelease);
+		lpr->pr_use_linux26 = use26;
 		mtx_unlock(&pr->pr_mtx);
 	} else {
 		mtx_lock(&osname_lock);
 		strcpy(linux_osrelease, osrelease);
+		linux_use_linux26 = use26;
 		mtx_unlock(&osname_lock);
 	}
 
diff --git a/sys/compat/linux/linux_mib.h b/sys/compat/linux/linux_mib.h
index 42d9d899266b..85f616352ad0 100644
--- a/sys/compat/linux/linux_mib.h
+++ b/sys/compat/linux/linux_mib.h
@@ -40,4 +40,6 @@ int	linux_set_osrelease(struct thread *td, char *osrelease);
 int	linux_get_oss_version(struct thread *td);
 int	linux_set_oss_version(struct thread *td, int oss_version);
 
+int	linux_use26(struct thread *td);
+
 #endif /* _LINUX_MIB_H_ */
diff --git a/sys/compat/linux/linux_misc.c b/sys/compat/linux/linux_misc.c
index 6fd69e066bf5..489b0790da64 100644
--- a/sys/compat/linux/linux_misc.c
+++ b/sys/compat/linux/linux_misc.c
@@ -1400,15 +1400,13 @@ int
 linux_getpid(struct thread *td, struct linux_getpid_args *args)
 {
 	struct linux_emuldata *em;
-	char osrel[LINUX_MAX_UTSNAME];
 
 #ifdef DEBUG
 	if (ldebug(getpid))
 		printf(ARGS(getpid, ""));
 #endif
 
-	linux_get_osrelease(td, osrel);
-	if (strlen(osrel) >= 3 && osrel[2] == '6') {
+	if (linux_use26(td)) {
 		em = em_find(td->td_proc, EMUL_UNLOCKED);
 		KASSERT(em != NULL, ("getpid: emuldata not found.\n"));
 		td->td_retval[0] = em->shared->group_pid;
@@ -1438,15 +1436,13 @@ linux_getppid(struct thread *td, struct linux_getppid_args *args)
 {
 	struct linux_emuldata *em;
 	struct proc *p, *pp;
-	char osrel[LINUX_MAX_UTSNAME];
 
 #ifdef DEBUG
 	if (ldebug(getppid))
 		printf(ARGS(getppid, ""));
 #endif
 
-	linux_get_osrelease(td, osrel);
-	if (strlen(osrel) >= 3 && osrel[2] != '6') {
+	if (!linux_use26(td)) {
 		PROC_LOCK(td->td_proc);
 		td->td_retval[0] = td->td_proc->p_pptr->p_pid;
 		PROC_UNLOCK(td->td_proc);
@@ -1573,15 +1569,13 @@ linux_exit_group(struct thread *td, struct linux_exit_group_args *args)
 {
 	struct linux_emuldata *em, *td_em, *tmp_em;
 	struct proc *sp;
-	char osrel[LINUX_MAX_UTSNAME];
 
 #ifdef DEBUG
 	if (ldebug(exit_group))
 		printf(ARGS(exit_group, "%i"), args->error_code);
 #endif
 
-	linux_get_osrelease(td, osrel);
-	if (strlen(osrel) >= 3 && osrel[2] == '6') {
+	if (linux_use26(td)) {
 		td_em = em_find(td->td_proc, EMUL_UNLOCKED);
 
 		KASSERT(td_em != NULL, ("exit_group: emuldata not found.\n"));