[PATCH] uml: physical memory map file fixes

UML really wants shared memory semantics form its physical memory map file,
and the place for that is /dev/shm. So move the default, and fix the error
messages to recognize that this value can be overridden.

Signed-off-by: Rob Landley <[e-mail]>
Signed-off-by: Jeff Dike <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/os-Linux/mem.c

···
 #include <fcntl.h>
 #include <sys/types.h>
 #include <sys/mman.h>
+#include <sys/statfs.h>
 #include "kern_util.h"
 #include "user.h"
 #include "user_util.h"
···
 
 #include <sys/param.h>
 
+static char *default_tmpdir = "/tmp";
 static char *tempdir = NULL;
 
 static void __init find_tempdir(void)
···
 			break;
 	}
 	if((dir == NULL) || (*dir == '\0'))
-		dir = "/tmp";
+		dir = default_tmpdir;
 
 	tempdir = malloc(strlen(dir) + 2);
 	if(tempdir == NULL){
···
 	}
 	strcpy(tempdir, dir);
 	strcat(tempdir, "/");
+}
+
+/* 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.
+ */
+static int next(int fd, char *buf, int size, char c)
+{
+	int n;
+	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';
+	}
+
+	ptr++;
+	memmove(buf, ptr, strlen(ptr) + 1);
+	return 1;
+}
+
+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.
+ */
+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, sizeof(buf) / sizeof(buf[0]), ' ');
+		if(found != 1)
+			break;
+
+		if(!strncmp(buf, "/dev/shm", strlen("/dev/shm")))
+			goto found;
+
+		found = next(fd, buf, sizeof(buf) / sizeof(buf[0]), '\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);
+
+	return;
+
+found:
+	found = next(fd, buf, sizeof(buf) / sizeof(buf[0]), ' ');
+	if(found != 1)
+		goto err;
+
+	if(strncmp(buf, "tmpfs", strlen("tmpfs"))){
+		printf("not tmpfs\n");
+		return;
+	}
+
+	printf("OK\n");
+	default_tmpdir = "/dev/shm";
 }
 
 /*
···
 	char *tempname;
 	int fd;
 
+	which_tmpdir();
 	tempname = malloc(MAXPATHLEN);
 
 	find_tempdir();
···
 		perror("exec_close");
 	}
 	return(fd);
+}
+
+
+void check_tmpexec(void)
+{
+	void *addr;
+	int err, fd = create_tmp_file(UM_KERN_PAGE_SIZE);
+
+	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);
+	if(addr == MAP_FAILED){
+		err = errno;
+		perror("failed");
+		if(err == EPERM)
+			printf("%s must be not mounted noexec\n",tempdir);
+		exit(1);
+	}
+	printf("OK\n");
+	munmap(addr, UM_KERN_PAGE_SIZE);
+
+	close(fd);
 }

arch/um/os-Linux/start_up.c

···
 	check_sysemu();
 }
 
-extern int create_tmp_file(unsigned long long len);
-
-static void check_tmpexec(void)
-{
-	void *addr;
-	int err, fd = create_tmp_file(UM_KERN_PAGE_SIZE);
-
-	addr = mmap(NULL, UM_KERN_PAGE_SIZE,
-		    PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, fd, 0);
-	printf("Checking PROT_EXEC mmap in /tmp...");
-	fflush(stdout);
-	if(addr == MAP_FAILED){
-		err = errno;
-		perror("failed");
-		if(err == EPERM)
-			printf("/tmp must be not mounted noexec\n");
-		exit(1);
-	}
-	printf("OK\n");
-	munmap(addr, UM_KERN_PAGE_SIZE);
-
-	close(fd);
-}
+extern void check_tmpexec(void);
 
 void os_early_checks(void)
 {