Merge branch 'for-linus-4.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml

Pull UML updates from Richard Weinberger:
 "Mostly fixes for UML:

   - First round of fixes for PTRACE_GETRESET/SETREGSET

   - A printf vs printk cleanup

   - Minor improvements"

* 'for-linus-4.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml:
  um: Correctly check for PTRACE_GETRESET/SETREGSET
  um: v2: Use generic NOTES macro
  um: Add kerneldoc for userspace_tramp() and start_userspace()
  um: Add kerneldoc for segv_handler
  um: stub-data.h: remove superfluous include
  um: userspace - be more verbose in ptrace set regs error
  um: add dummy ioremap and iounmap functions
  um: Allow building and running on older hosts
  um: Avoid longjmp/setjmp symbol clashes with libpthread.a
  um: console: Ignore console= option
  um: Use os_warn to print out pre-boot warning/error messages
  um: Add os_warn() for pre-boot warning/error messages
  um: Use os_info for the messages on normal path
  um: Add os_info() for pre-boot information messages
  um: Use printk instead of printf in make_uml_dir

17 files changed, 172 insertions, 61 deletions

diff --git a/arch/um/Makefile b/arch/um/Makefile
index 0ca46ededfc7..6ca4f66085c1 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -59,10 +59,14 @@ KBUILD_CPPFLAGS += -I$(srctree)/$(HOST_DIR)/um
 # Same things for in6addr_loopback and mktime - found in libc. For these two we
 # only get link-time error, luckily.
 #
+# -Dlongjmp=kernel_longjmp prevents anything from referencing the libpthread.a
+# embedded copy of longjmp, same thing for setjmp.
+#
 # These apply to USER_CFLAGS to.
 
 KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ \
 	$(ARCH_INCLUDE) $(MODE_INCLUDE) -Dvmap=kernel_vmap	\
+	-Dlongjmp=kernel_longjmp -Dsetjmp=kernel_setjmp \
 	-Din6addr_loopback=kernel_in6addr_loopback \
 	-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr
 
diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
index 7b361f36ca96..c90817b04da9 100644
--- a/arch/um/drivers/stdio_console.c
+++ b/arch/um/drivers/stdio_console.c
@@ -192,6 +192,9 @@ __uml_exitcall(console_exit);
 
 static int console_chan_setup(char *str)
 {
+	if (!strncmp(str, "sole=", 5))	/* console= option specifies tty */
+		return 0;
+
 	line_setup(vt_conf, MAX_TTYS, &def_conf, str, "console");
 	return 1;
 }
diff --git a/arch/um/include/asm/common.lds.S b/arch/um/include/asm/common.lds.S
index 133055311dce..9e6d5997cfc4 100644
--- a/arch/um/include/asm/common.lds.S
+++ b/arch/um/include/asm/common.lds.S
@@ -15,7 +15,7 @@
   PROVIDE (_unprotected_end = .);
 
   . = ALIGN(4096);
-  .note : { *(.note.*) }
+  NOTES
   EXCEPTION_TABLE(0)
 
   BUG_TABLE
diff --git a/arch/um/include/asm/io.h b/arch/um/include/asm/io.h
new file mode 100644
index 000000000000..8f35d574f35b
--- /dev/null
+++ b/arch/um/include/asm/io.h
@@ -0,0 +1,17 @@
+#ifndef _ASM_UM_IO_H
+#define _ASM_UM_IO_H
+
+#define ioremap ioremap
+static inline void __iomem *ioremap(phys_addr_t offset, size_t size)
+{
+	return (void __iomem *)(unsigned long)offset;
+}
+
+#define iounmap iounmap
+static inline void iounmap(void __iomem *addr)
+{
+}
+
+#include <asm-generic/io.h>
+
+#endif
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index cd1fa97776c3..574e03fc7ba2 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -242,6 +242,10 @@ extern void setup_hostinfo(char *buf, int len);
 extern void os_dump_core(void) __attribute__ ((noreturn));
 extern void um_early_printk(const char *s, unsigned int n);
 extern void os_fix_helper_signals(void);
+extern void os_info(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
+extern void os_warn(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
 
 /* time.c */
 extern void os_idle_sleep(unsigned long long nsecs);
diff --git a/arch/um/include/shared/skas/stub-data.h b/arch/um/include/shared/skas/stub-data.h
index a9deece956bf..13f404e1262b 100644
--- a/arch/um/include/shared/skas/stub-data.h
+++ b/arch/um/include/shared/skas/stub-data.h
@@ -8,8 +8,6 @@
 #ifndef __STUB_DATA_H
 #define __STUB_DATA_H
 
-#include <time.h>
-
 struct stub_data {
 	unsigned long offset;
 	int fd;
diff --git a/arch/um/kernel/physmem.c b/arch/um/kernel/physmem.c
index 4c9861b421fd..f02596e9931d 100644
--- a/arch/um/kernel/physmem.c
+++ b/arch/um/kernel/physmem.c
@@ -89,8 +89,8 @@ void __init setup_physmem(unsigned long start, unsigned long reserve_end,
 	offset = uml_reserved - uml_physmem;
 	map_size = len - offset;
 	if(map_size <= 0) {
-		printf("Too few physical memory! Needed=%d, given=%d\n",
-		       offset, len);
+		os_warn("Too few physical memory! Needed=%lu, given=%lu\n",
+			offset, len);
 		exit(1);
 	}
 
@@ -99,9 +99,9 @@ void __init setup_physmem(unsigned long start, unsigned long reserve_end,
 	err = os_map_memory((void *) uml_reserved, physmem_fd, offset,
 			    map_size, 1, 1, 1);
 	if (err < 0) {
-		printf("setup_physmem - mapping %ld bytes of memory at 0x%p "
-		       "failed - errno = %d\n", map_size,
-		       (void *) uml_reserved, err);
+		os_warn("setup_physmem - mapping %ld bytes of memory at 0x%p "
+			"failed - errno = %d\n", map_size,
+			(void *) uml_reserved, err);
 		exit(1);
 	}
 
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 59158871b9fc..4e6fcb32620f 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -183,6 +183,16 @@ void fatal_sigsegv(void)
 	os_dump_core();
 }
 
+/**
+ * segv_handler() - the SIGSEGV handler
+ * @sig:	the signal number
+ * @unused_si:	the signal info struct; unused in this handler
+ * @regs:	the ptrace register information
+ *
+ * The handler first extracts the faultinfo from the UML ptrace regs struct.
+ * If the userfault did not happen in an UML userspace process, bad_segv is called.
+ * Otherwise the signal did happen in a cloned userspace process, handle it.
+ */
 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 {
 	struct faultinfo * fi = UPT_FAULTINFO(regs);
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 7b5640117325..f433690b9b37 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -34,7 +34,7 @@ static char __initdata command_line[COMMAND_LINE_SIZE] = { 0 };
 static void __init add_arg(char *arg)
 {
 	if (strlen(command_line) + strlen(arg) + 1 > COMMAND_LINE_SIZE) {
-		printf("add_arg: Too many command line arguments!\n");
+		os_warn("add_arg: Too many command line arguments!\n");
 		exit(1);
 	}
 	if (strlen(command_line) > 0)
@@ -120,6 +120,7 @@ static const char *usage_string =
 
 static int __init uml_version_setup(char *line, int *add)
 {
+	/* Explicitly use printf() to show version in stdout */
 	printf("%s\n", init_utsname()->release);
 	exit(0);
 
@@ -148,8 +149,8 @@ __uml_setup("root=", uml_root_setup,
 
 static int __init no_skas_debug_setup(char *line, int *add)
 {
-	printf("'debug' is not necessary to gdb UML in skas mode - run \n");
-	printf("'gdb linux'\n");
+	os_warn("'debug' is not necessary to gdb UML in skas mode - run\n");
+	os_warn("'gdb linux'\n");
 
 	return 0;
 }
@@ -165,6 +166,7 @@ static int __init Usage(char *line, int *add)
 
 	printf(usage_string, init_utsname()->release);
 	p = &__uml_help_start;
+	/* Explicitly use printf() to show help in stdout */
 	while (p < &__uml_help_end) {
 		printf("%s", *p);
 		p++;
@@ -283,8 +285,8 @@ int __init linux_main(int argc, char **argv)
 
 	diff = UML_ROUND_UP(brk_start) - UML_ROUND_UP(&_end);
 	if (diff > 1024 * 1024) {
-		printf("Adding %ld bytes to physical memory to account for "
-		       "exec-shield gap\n", diff);
+		os_info("Adding %ld bytes to physical memory to account for "
+			"exec-shield gap\n", diff);
 		physmem_size += UML_ROUND_UP(brk_start) - UML_ROUND_UP(&_end);
 	}
 
@@ -324,8 +326,8 @@ int __init linux_main(int argc, char **argv)
 	end_vm = start_vm + virtmem_size;
 
 	if (virtmem_size < physmem_size)
-		printf("Kernel virtual memory size shrunk to %lu bytes\n",
-		       virtmem_size);
+		os_info("Kernel virtual memory size shrunk to %lu bytes\n",
+			virtmem_size);
 
 	os_flush_stdout();
 
diff --git a/arch/um/kernel/umid.c b/arch/um/kernel/umid.c
index f6cc3bd61781..10bf4aca529f 100644
--- a/arch/um/kernel/umid.c
+++ b/arch/um/kernel/umid.c
@@ -16,14 +16,14 @@ static int __init set_umid_arg(char *name, int *add)
 	int err;
 
 	if (umid_inited) {
-		printf("umid already set\n");
+		os_warn("umid already set\n");
 		return 0;
 	}
 
 	*add = 0;
 	err = set_umid(name);
 	if (err == -EEXIST)
-		printf("umid '%s' already in use\n", name);
+		os_warn("umid '%s' already in use\n", name);
 	else if (!err)
 		umid_inited = 1;
 
diff --git a/arch/um/os-Linux/execvp.c b/arch/um/os-Linux/execvp.c
index 8fb25ca07c46..84a0777c2a45 100644
--- a/arch/um/os-Linux/execvp.c
+++ b/arch/um/os-Linux/execvp.c
@@ -136,7 +136,7 @@ int main(int argc, char**argv)
 	int ret;
 	argc--;
 	if (!argc) {
-		fprintf(stderr, "Not enough arguments\n");
+		os_warn("Not enough arguments\n");
 		return 1;
 	}
 	argv++;
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index 9d499de87e63..5f970ece5ac3 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -74,8 +74,8 @@ static void install_fatal_handler(int sig)
 	action.sa_restorer = NULL;
 	action.sa_handler = last_ditch_exit;
 	if (sigaction(sig, &action, NULL) < 0) {
-		printf("failed to install handler for signal %d - errno = %d\n",
-		       sig, errno);
+		os_warn("failed to install handler for signal %d "
+			"- errno = %d\n", sig, errno);
 		exit(1);
 	}
 }
@@ -175,7 +175,7 @@ int __init main(int argc, char **argv, char **envp)
 	/* disable SIGIO for the fds and set SIGIO to be ignored */
 	err = deactivate_all_fds();
 	if (err)
-		printf("deactivate_all_fds failed, errno = %d\n", -err);
+		os_warn("deactivate_all_fds failed, errno = %d\n", -err);
 
 	/*
 	 * Let any pending signals fire now.  This ensures
@@ -184,14 +184,13 @@ int __init main(int argc, char **argv, char **envp)
 	 */
 	unblock_signals();
 
+	os_info("\n");
 	/* Reboot */
 	if (ret) {
-		printf("\n");
 		execvp(new_argv[0], new_argv);
 		perror("Failed to exec kernel");
 		ret = 1;
 	}
-	printf("\n");
 	return uml_exitcode;
 }
 
diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index 8b1767668515..e162a95ad7dd 100644
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -25,13 +25,13 @@ static int __init check_tmpfs(const char *dir)
 {
 	struct statfs st;
 
-	printf("Checking if %s is on tmpfs...", dir);
+	os_info("Checking if %s is on tmpfs...", dir);
 	if (statfs(dir, &st) < 0) {
-		printf("%s\n", strerror(errno));
+		os_info("%s\n", strerror(errno));
 	} else if (st.f_type != TMPFS_MAGIC) {
-		printf("no\n");
+		os_info("no\n");
 	} else {
-		printf("OK\n");
+		os_info("OK\n");
 		return 0;
 	}
 	return -1;
@@ -61,18 +61,18 @@ static char * __init choose_tempdir(void)
 	int i;
 	const char *dir;
 
-	printf("Checking environment variables for a tempdir...");
+	os_info("Checking environment variables for a tempdir...");
 	for (i = 0; vars[i]; i++) {
 		dir = getenv(vars[i]);
 		if ((dir != NULL) && (*dir != '\0')) {
-			printf("%s\n", dir);
+			os_info("%s\n", dir);
 			if (check_tmpfs(dir) >= 0)
 				goto done;
 			else
 				goto warn;
 		}
 	}
-	printf("none found\n");
+	os_info("none found\n");
 
 	for (i = 0; tmpfs_dirs[i]; i++) {
 		dir = tmpfs_dirs[i];
@@ -82,7 +82,7 @@ static char * __init choose_tempdir(void)
 
 	dir = fallback_dir;
 warn:
-	printf("Warning: tempdir %s is not on tmpfs\n", dir);
+	os_warn("Warning: tempdir %s is not on tmpfs\n", dir);
 done:
 	/* Make a copy since getenv results may not remain valid forever. */
 	return strdup(dir);
@@ -100,7 +100,7 @@ static int __init make_tempfile(const char *template)
 	if (tempdir == NULL) {
 		tempdir = choose_tempdir();
 		if (tempdir == NULL) {
-			fprintf(stderr, "Failed to choose tempdir: %s\n",
+			os_warn("Failed to choose tempdir: %s\n",
 				strerror(errno));
 			return -1;
 		}
@@ -125,7 +125,7 @@ static int __init make_tempfile(const char *template)
 	strcat(tempname, template);
 	fd = mkstemp(tempname);
 	if (fd < 0) {
-		fprintf(stderr, "open - cannot create %s: %s\n", tempname,
+		os_warn("open - cannot create %s: %s\n", tempname,
 			strerror(errno));
 		goto out;
 	}
@@ -194,16 +194,16 @@ void __init check_tmpexec(void)
 
 	addr = mmap(NULL, UM_KERN_PAGE_SIZE,
 		    PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, fd, 0);
-	printf("Checking PROT_EXEC mmap in %s...", tempdir);
+	os_info("Checking PROT_EXEC mmap in %s...", tempdir);
 	if (addr == MAP_FAILED) {
 		err = errno;
-		printf("%s\n", strerror(err));
+		os_warn("%s\n", strerror(err));
 		close(fd);
 		if (err == EPERM)
-			printf("%s must be not mounted noexec\n", tempdir);
+			os_warn("%s must be not mounted noexec\n", tempdir);
 		exit(1);
 	}
-	printf("OK\n");
+	os_info("OK\n");
 	munmap(addr, UM_KERN_PAGE_SIZE);
 
 	close(fd);
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 03b3c4cc7735..819d68656673 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -108,7 +108,7 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi)
 	wait_stub_done(pid);
 
 	/*
-	 * faultinfo is prepared by the stub-segv-handler at start of
+	 * faultinfo is prepared by the stub_segv_handler at start of
 	 * the stub stack page. We just have to copy it.
 	 */
 	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
@@ -175,6 +175,21 @@ static void handle_trap(int pid, struct uml_pt_regs *regs,
 
 extern char __syscall_stub_start[];
 
+/**
+ * userspace_tramp() - userspace trampoline
+ * @stack:	pointer to the new userspace stack page, can be NULL, if? FIXME:
+ *
+ * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
+ * This function will run on a temporary stack page.
+ * It ptrace()'es itself, then
+ * Two pages are mapped into the userspace address space:
+ * - STUB_CODE (with EXEC), which contains the skas stub code
+ * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
+ * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
+ * And last the process stops itself to give control to the UML kernel for this userspace process.
+ *
+ * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
+ */
 static int userspace_tramp(void *stack)
 {
 	void *addr;
@@ -236,12 +251,24 @@ static int userspace_tramp(void *stack)
 
 int userspace_pid[NR_CPUS];
 
+/**
+ * start_userspace() - prepare a new userspace process
+ * @stub_stack:	pointer to the stub stack. Can be NULL, if? FIXME:
+ *
+ * Setups a new temporary stack page that is used while userspace_tramp() runs
+ * Clones the kernel process into a new userspace process, with FDs only.
+ *
+ * Return: When positive: the process id of the new userspace process,
+ *         when negative: an error number.
+ * FIXME: can PIDs become negative?!
+ */
 int start_userspace(unsigned long stub_stack)
 {
 	void *stack;
 	unsigned long sp;
 	int pid, status, n, flags, err;
 
+	/* setup a temporary stack page */
 	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
 		     PROT_READ | PROT_WRITE | PROT_EXEC,
 		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
@@ -252,10 +279,12 @@ int start_userspace(unsigned long stub_stack)
 		return err;
 	}
 
+	/* set stack pointer to the end of the stack page, so it can grow downwards */
 	sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 
 	flags = CLONE_FILES | SIGCHLD;
 
+	/* clone into new userspace process */
 	pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 	if (pid < 0) {
 		err = -errno;
@@ -323,11 +352,17 @@ void userspace(struct uml_pt_regs *regs)
 		 * fail.  In this case, there is nothing to do but
 		 * just kill the process.
 		 */
-		if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
+		if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
+			printk(UM_KERN_ERR "userspace - ptrace set regs "
+			       "failed, errno = %d\n", errno);
 			fatal_sigsegv();
+		}
 
-		if (put_fp_registers(pid, regs->fp))
+		if (put_fp_registers(pid, regs->fp)) {
+			printk(UM_KERN_ERR "userspace - ptrace set fp regs "
+			       "failed, errno = %d\n", errno);
 			fatal_sigsegv();
+		}
 
 		/* Now we set local_using_sysemu to be used for one loop */
 		local_using_sysemu = get_using_sysemu();
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 22a358ef1b0c..b1b6b75c5b17 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -166,7 +166,7 @@ static void __init check_sysemu(void)
 	unsigned long regs[MAX_REG_NR];
 	int pid, n, status, count=0;
 
-	non_fatal("Checking syscall emulation patch for ptrace...");
+	os_info("Checking syscall emulation patch for ptrace...");
 	sysemu_supported = 0;
 	pid = start_ptraced_child();
 
@@ -199,10 +199,10 @@ static void __init check_sysemu(void)
 		goto fail_stopped;
 
 	sysemu_supported = 1;
-	non_fatal("OK\n");
+	os_info("OK\n");
 	set_using_sysemu(!force_sysemu_disabled);
 
-	non_fatal("Checking advanced syscall emulation patch for ptrace...");
+	os_info("Checking advanced syscall emulation patch for ptrace...");
 	pid = start_ptraced_child();
 
 	if ((ptrace(PTRACE_OLDSETOPTIONS, pid, 0,
@@ -244,7 +244,7 @@ static void __init check_sysemu(void)
 		goto fail_stopped;
 
 	sysemu_supported = 2;
-	non_fatal("OK\n");
+	os_info("OK\n");
 
 	if (!force_sysemu_disabled)
 		set_using_sysemu(sysemu_supported);
@@ -260,7 +260,7 @@ static void __init check_ptrace(void)
 {
 	int pid, syscall, n, status;
 
-	non_fatal("Checking that ptrace can change system call numbers...");
+	os_info("Checking that ptrace can change system call numbers...");
 	pid = start_ptraced_child();
 
 	if ((ptrace(PTRACE_OLDSETOPTIONS, pid, 0,
@@ -292,7 +292,7 @@ static void __init check_ptrace(void)
 		}
 	}
 	stop_ptraced_child(pid, 0, 1);
-	non_fatal("OK\n");
+	os_info("OK\n");
 	check_sysemu();
 }
 
@@ -308,15 +308,17 @@ static void __init check_coredump_limit(void)
 		return;
 	}
 
-	printf("Core dump limits :\n\tsoft - ");
+	os_info("Core dump limits :\n\tsoft - ");
 	if (lim.rlim_cur == RLIM_INFINITY)
-		printf("NONE\n");
-	else printf("%lu\n", lim.rlim_cur);
+		os_info("NONE\n");
+	else
+		os_info("%llu\n", (unsigned long long)lim.rlim_cur);
 
-	printf("\thard - ");
+	os_info("\thard - ");
 	if (lim.rlim_max == RLIM_INFINITY)
-		printf("NONE\n");
-	else printf("%lu\n", lim.rlim_max);
+		os_info("NONE\n");
+	else
+		os_info("%llu\n", (unsigned long long)lim.rlim_max);
 }
 
 void __init os_early_checks(void)
@@ -349,7 +351,7 @@ int __init parse_iomem(char *str, int *add)
 	driver = str;
 	file = strchr(str,',');
 	if (file == NULL) {
-		fprintf(stderr, "parse_iomem : failed to parse iomem\n");
+		os_warn("parse_iomem : failed to parse iomem\n");
 		goto out;
 	}
 	*file = '\0';
diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index c1dc89261f67..998fbb445458 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -35,8 +35,9 @@ static int __init make_uml_dir(void)
 
 		err = -ENOENT;
 		if (home == NULL) {
-			printk(UM_KERN_ERR "make_uml_dir : no value in "
-			       "environment for $HOME\n");
+			printk(UM_KERN_ERR
+				"%s: no value in environment for $HOME\n",
+				__func__);
 			goto err;
 		}
 		strlcpy(dir, home, sizeof(dir));
@@ -50,13 +51,15 @@ static int __init make_uml_dir(void)
 	err = -ENOMEM;
 	uml_dir = malloc(strlen(dir) + 1);
 	if (uml_dir == NULL) {
-		printf("make_uml_dir : malloc failed, errno = %d\n", errno);
+		printk(UM_KERN_ERR "%s : malloc failed, errno = %d\n",
+			__func__, errno);
 		goto err;
 	}
 	strcpy(uml_dir, dir);
 
 	if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
-	        printf("Failed to mkdir '%s': %s\n", uml_dir, strerror(errno));
+		printk(UM_KERN_ERR "Failed to mkdir '%s': %s\n",
+			uml_dir, strerror(errno));
 		err = -errno;
 		goto err_free;
 	}
@@ -351,7 +354,7 @@ char *get_umid(void)
 static int __init set_uml_dir(char *name, int *add)
 {
 	if (*name == '\0') {
-		printf("uml_dir can't be an empty string\n");
+		os_warn("uml_dir can't be an empty string\n");
 		return 0;
 	}
 
@@ -362,7 +365,7 @@ static int __init set_uml_dir(char *name, int *add)
 
 	uml_dir = malloc(strlen(name) + 2);
 	if (uml_dir == NULL) {
-		printf("Failed to malloc uml_dir - error = %d\n", errno);
+		os_warn("Failed to malloc uml_dir - error = %d\n", errno);
 
 		/*
 		 * Return 0 here because do_initcalls doesn't look at
@@ -387,8 +390,8 @@ static void remove_umid_dir(void)
 	sprintf(dir, "%s%s", uml_dir, umid);
 	err = remove_files_and_dir(dir);
 	if (err)
-		printf("remove_umid_dir - remove_files_and_dir failed with "
-		       "err = %d\n", err);
+		os_warn("%s - remove_files_and_dir failed with err = %d\n",
+			__func__, err);
 }
 
 __uml_exitcall(remove_umid_dir);
diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index faee55ef6d2f..8cc8b2617a67 100644
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -13,6 +13,7 @@
 #include <wait.h>
 #include <sys/mman.h>
 #include <sys/utsname.h>
+#include <init.h>
 #include <os.h>
 
 void stack_protections(unsigned long address)
@@ -152,3 +153,36 @@ void um_early_printk(const char *s, unsigned int n)
 {
 	printf("%.*s", n, s);
 }
+
+static int quiet_info;
+
+static int __init quiet_cmd_param(char *str, int *add)
+{
+	quiet_info = 1;
+	return 0;
+}
+
+__uml_setup("quiet", quiet_cmd_param,
+"quiet\n"
+"    Turns off information messages during boot.\n\n");
+
+void os_info(const char *fmt, ...)
+{
+	va_list list;
+
+	if (quiet_info)
+		return;
+
+	va_start(list, fmt);
+	vfprintf(stderr, fmt, list);
+	va_end(list);
+}
+
+void os_warn(const char *fmt, ...)
+{
+	va_list list;
+
+	va_start(list, fmt);
+	vfprintf(stderr, fmt, list);
+	va_end(list);
+}