modutils: add FEATURE_INSMOD_TRY_MMAP option

[platform/upstream/busybox.git] / modutils / modutils.c

diff --git a/modutils/modutils.c b/modutils/modutils.c
index 969926d..850a868 100644 (file)
--- a/modutils/modutils.c
+++ b/modutils/modutils.c
@@ -62,7 +62,7 @@ char* FAST_FUNC filename2modname(const char *filename, char *modname)
        return modname;
 }
 
-char * FAST_FUNC parse_cmdline_module_options(char **argv)
+char* FAST_FUNC parse_cmdline_module_options(char **argv)
 {
        char *options;
        int optlen;
@@ -77,6 +77,40 @@ char * FAST_FUNC parse_cmdline_module_options(char **argv)
        return options;
 }
 
+#if ENABLE_FEATURE_INSMOD_TRY_MMAP
+void* FAST_FUNC try_to_mmap_module(const char *filename, size_t *image_size_p)
+{
+       /* We have user reports of failure to load 3MB module
+        * on a 16MB RAM machine. Apparently even a transient
+        * memory spike to 6MB during module load
+        * is too big for that system. */
+       void *image;
+       struct stat st;
+       int fd;
+
+       fd = xopen(filename, O_RDONLY);
+       fstat(fd, &st);
+       image = NULL;
+       /* st.st_size is off_t, we can't just pass it to mmap */
+       if (st.st_size <= *image_size_p) {
+               size_t image_size = st.st_size;
+               image = mmap(NULL, image_size, PROT_READ, MAP_PRIVATE, fd, 0);
+               if (image == MAP_FAILED) {
+                       image = NULL;
+               } else if (*(uint32_t*)image != SWAP_BE32(0x7f454C46)) {
+                       /* No ELF signature. Compressed module? */
+                       munmap(image, image_size);
+                       image = NULL;
+               } else {
+                       /* Success. Report the size */
+                       *image_size_p = image_size;
+               }
+       }
+       close(fd);
+       return image;
+}
+#endif
+
 /* Return:
  * 0 on success,
  * -errno on open/read error,
@@ -84,9 +118,10 @@ char * FAST_FUNC parse_cmdline_module_options(char **argv)
  */
 int FAST_FUNC bb_init_module(const char *filename, const char *options)
 {
-       size_t len;
+       size_t image_size;
        char *image;
        int rc;
+       bool mmaped;
 
        if (!options)
                options = "";
@@ -97,17 +132,25 @@ int FAST_FUNC bb_init_module(const char *filename, const char *options)
                return bb_init_module_24(filename, options);
 #endif
 
-       /* Use the 2.6 way */
-       len = INT_MAX - 4095;
-       errno = ENOMEM; /* may be changed by e.g. open errors below */
-       image = xmalloc_open_zipped_read_close(filename, &len);
-       if (!image)
-               return -errno;
+       image_size = INT_MAX - 4095;
+       mmaped = 0;
+       image = try_to_mmap_module(filename, &image_size);
+       if (image) {
+               mmaped = 1;
+       } else {
+               errno = ENOMEM; /* may be changed by e.g. open errors below */
+               image = xmalloc_open_zipped_read_close(filename, &image_size);
+               if (!image)
+                       return -errno;
+       }
 
        errno = 0;
-       init_module(image, len, options);
+       init_module(image, image_size, options);
        rc = errno;
-       free(image);
+       if (mmaped)
+               munmap(image, image_size);
+       else
+               free(image);
        return rc;
 }