[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 <rob@landley.net>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index 71bb90a..c6432e7 100644 (file)
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -8,6 +8,7 @@
 #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"
@@ -19,6 +20,7 @@
 
 #include <sys/param.h>
 
+static char *default_tmpdir = "/tmp";
 static char *tempdir = NULL;
 
 static void __init find_tempdir(void)
@@ -34,7 +36,7 @@ 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){
@@ -46,6 +48,96 @@ static void __init find_tempdir(void)
        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";
+}
+
 /*
  * This proc still used in tt-mode
  * (file: kernel/tt/ptproxy/proxy.c, proc: start_debugger).
@@ -56,6 +148,7 @@ int make_tempfile(const char *template, char **out_tempname, int do_unlink)
        char *tempname;
        int fd;
 
+       which_tmpdir();
        tempname = malloc(MAXPATHLEN);
 
        find_tempdir();
@@ -137,3 +230,26 @@ int create_mem_file(unsigned long long len)
        }
        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);
+}

diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 387e26a..5031485 100644 (file)
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -296,29 +296,7 @@ static void __init check_ptrace(void)
        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)
 {