[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>

2 files changed, 118 insertions, 24 deletions

diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index 71bb90a7606d..c6432e729241 100644
--- 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 387e26af301a..503148504009 100644
--- 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)
 {