1 files changed, 86 insertions, 160 deletions

diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index e696144d2be..897e9ad0c10 100644
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -12,205 +12,133 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/mman.h>
-#include <sys/param.h>
-#include "init.h"
-#include "kern_constants.h"
-#include "os.h"
-#include "user.h"
+#include <sys/vfs.h>
+#include <linux/magic.h>
+#include <init.h>
+#include <os.h>
 
-/* Modified by which_tmpdir, which is called during early boot */
-static char *default_tmpdir = "/tmp";
-
-/*
- *  Modified when creating the physical memory file and when checking
- * the tmp filesystem for usability, both happening during early boot.
- */
+/* Set by make_tempfile() during early boot. */
 static char *tempdir = NULL;
 
-static void __init find_tempdir(void)
+/* Check if dir is on tmpfs. Return 0 if yes, -1 if no or error. */
+static int __init check_tmpfs(const char *dir)
 {
-	const char *dirs[] = { "TMP", "TEMP", "TMPDIR", NULL };
-	int i;
-	char *dir = NULL;
-
-	if (tempdir != NULL)
-		/* We've already been called */
-		return;
-	for (i = 0; dirs[i]; i++) {
-		dir = getenv(dirs[i]);
-		if ((dir != NULL) && (*dir != '\0'))
-			break;
+	struct statfs st;
+
+	printf("Checking if %s is on tmpfs...", dir);
+	if (statfs(dir, &st) < 0) {
+		printf("%s\n", strerror(errno));
+	} else if (st.f_type != TMPFS_MAGIC) {
+		printf("no\n");
+	} else {
+		printf("OK\n");
+		return 0;
 	}
-	if ((dir == NULL) || (*dir == '\0'))
-		dir = default_tmpdir;
-
-	tempdir = malloc(strlen(dir) + 2);
-	if (tempdir == NULL) {
-		fprintf(stderr, "Failed to malloc tempdir, "
-			"errno = %d\n", errno);
-		return;
-	}
-	strcpy(tempdir, dir);
-	strcat(tempdir, "/");
+	return -1;
 }
 
 /*
- * This will return 1, with the first character in buf being the
- * character following the next instance of c in the file.  This will
- * read the file as needed.  If there's an error, -errno is returned;
- * if the end of the file is reached, 0 is returned.
+ * Choose the tempdir to use. We want something on tmpfs so that our memory is
+ * not subject to the host's vm.dirty_ratio. If a tempdir is specified in the
+ * environment, we use that even if it's not on tmpfs, but we warn the user.
+ * Otherwise, we try common tmpfs locations, and if no tmpfs directory is found
+ * then we fall back to /tmp.
  */
-static int next(int fd, char *buf, size_t size, char c)
+static char * __init choose_tempdir(void)
 {
-	ssize_t n;
-	size_t len;
-	char *ptr;
-
-	while ((ptr = strchr(buf, c)) == NULL) {
-		n = read(fd, buf, size - 1);
-		if (n == 0)
-			return 0;
-		else if (n < 0)
-			return -errno;
-
-		buf[n] = '\0';
+	static const char * const vars[] = {
+		"TMPDIR",
+		"TMP",
+		"TEMP",
+		NULL
+	};
+	static const char fallback_dir[] = "/tmp";
+	static const char * const tmpfs_dirs[] = {
+		"/dev/shm",
+		fallback_dir,
+		NULL
+	};
+	int i;
+	const char *dir;
+
+	printf("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);
+			if (check_tmpfs(dir) >= 0)
+				goto done;
+			else
+				goto warn;
+		}
 	}
+	printf("none found\n");
 
-	ptr++;
-	len = strlen(ptr);
-	memmove(buf, ptr, len + 1);
-
-	/*
-	 * Refill the buffer so that if there's a partial string that we care
-	 * about, it will be completed, and we can recognize it.
-	 */
-	n = read(fd, &buf[len], size - len - 1);
-	if (n < 0)
-		return -errno;
+	for (i = 0; tmpfs_dirs[i]; i++) {
+		dir = tmpfs_dirs[i];
+		if (check_tmpfs(dir) >= 0)
+			goto done;
+	}
 
-	buf[len + n] = '\0';
-	return 1;
+	dir = fallback_dir;
+warn:
+	printf("Warning: tempdir %s is not on tmpfs\n", dir);
+done:
+	/* Make a copy since getenv results may not remain valid forever. */
+	return strdup(dir);
 }
 
-/* which_tmpdir is called only during early boot */
-static int checked_tmpdir = 0;
-
 /*
- * Look for a tmpfs mounted at /dev/shm.  I couldn't find a cleaner
- * way to do this than to parse /proc/mounts.  statfs will return the
- * same filesystem magic number and fs id for both /dev and /dev/shm
- * when they are both tmpfs, so you can't tell if they are different
- * filesystems.  Also, there seems to be no other way of finding the
- * mount point of a filesystem from within it.
- *
- * If a /dev/shm tmpfs entry is found, then we switch to using it.
- * Otherwise, we stay with the default /tmp.
+ * Create an unlinked tempfile in a suitable tempdir. template must be the
+ * basename part of the template with a leading '/'.
  */
-static void which_tmpdir(void)
-{
-	int fd, found;
-	char buf[128] = { '\0' };
-
-	if (checked_tmpdir)
-		return;
-
-	checked_tmpdir = 1;
-
-	printf("Checking for tmpfs mount on /dev/shm...");
-
-	fd = open("/proc/mounts", O_RDONLY);
-	if (fd < 0) {
-		printf("failed to open /proc/mounts, errno = %d\n", errno);
-		return;
-	}
-
-	while (1) {
-		found = next(fd, buf, ARRAY_SIZE(buf), ' ');
-		if (found != 1)
-			break;
-
-		if (!strncmp(buf, "/dev/shm", strlen("/dev/shm")))
-			goto found;
-
-		found = next(fd, buf, ARRAY_SIZE(buf), '\n');
-		if (found != 1)
-			break;
-	}
-
-err:
-	if (found == 0)
-		printf("nothing mounted on /dev/shm\n");
-	else if (found < 0)
-		printf("read returned errno %d\n", -found);
-
-out:
-	close(fd);
-
-	return;
-
-found:
-	found = next(fd, buf, ARRAY_SIZE(buf), ' ');
-	if (found != 1)
-		goto err;
-
-	if (strncmp(buf, "tmpfs", strlen("tmpfs"))) {
-		printf("not tmpfs\n");
-		goto out;
-	}
-
-	printf("OK\n");
-	default_tmpdir = "/dev/shm";
-	goto out;
-}
-
-static int __init make_tempfile(const char *template, char **out_tempname,
-				int do_unlink)
+static int __init make_tempfile(const char *template)
 {
 	char *tempname;
 	int fd;
 
-	which_tmpdir();
-	tempname = malloc(MAXPATHLEN);
-	if (tempname == NULL)
-		return -1;
+	if (tempdir == NULL) {
+		tempdir = choose_tempdir();
+		if (tempdir == NULL) {
+			fprintf(stderr, "Failed to choose tempdir: %s\n",
+				strerror(errno));
+			return -1;
+		}
+	}
 
-	find_tempdir();
-	if ((tempdir == NULL) || (strlen(tempdir) >= MAXPATHLEN))
+	tempname = malloc(strlen(tempdir) + strlen(template) + 1);
+	if (tempname == NULL)
 		return -1;
 
-	if (template[0] != '/')
-		strcpy(tempname, tempdir);
-	else
-		tempname[0] = '\0';
-	strncat(tempname, template, MAXPATHLEN-1-strlen(tempname));
+	strcpy(tempname, tempdir);
+	strcat(tempname, template);
 	fd = mkstemp(tempname);
 	if (fd < 0) {
 		fprintf(stderr, "open - cannot create %s: %s\n", tempname,
 			strerror(errno));
 		goto out;
 	}
-	if (do_unlink && (unlink(tempname) < 0)) {
+	if (unlink(tempname) < 0) {
 		perror("unlink");
-		goto out;
+		goto close;
 	}
-	if (out_tempname) {
-		*out_tempname = tempname;
-	} else
-		free(tempname);
+	free(tempname);
 	return fd;
+close:
+	close(fd);
 out:
 	free(tempname);
 	return -1;
 }
 
-#define TEMPNAME_TEMPLATE "vm_file-XXXXXX"
+#define TEMPNAME_TEMPLATE "/vm_file-XXXXXX"
 
 static int __init create_tmp_file(unsigned long long len)
 {
 	int fd, err;
 	char zero;
 
-	fd = make_tempfile(TEMPNAME_TEMPLATE, NULL, 1);
+	fd = make_tempfile(TEMPNAME_TEMPLATE);
 	if (fd < 0)
 		exit(1);
 
@@ -254,7 +182,6 @@ int __init create_mem_file(unsigned long long len)
 	return fd;
 }
 
-
 void __init check_tmpexec(void)
 {
 	void *addr;
@@ -262,14 +189,13 @@ 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);
-	fflush(stdout);
+	printf("Checking PROT_EXEC mmap in %s...", tempdir);
 	if (addr == MAP_FAILED) {
 		err = errno;
-		perror("failed");
+		printf("%s\n", strerror(err));
 		close(fd);
 		if (err == EPERM)
-			printf("%s must be not mounted noexec\n",tempdir);
+			printf("%s must be not mounted noexec\n", tempdir);
 		exit(1);
 	}
 	printf("OK\n");