modutils: add FEATURE_INSMOD_TRY_MMAP option

function                                             old     new   delta
try_to_mmap_module                                     -     121    +121
bb_init_module_24                                   4514    4578     +64
bb_init_module                                       119     173     +54
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/0 up/down: 239/0)             Total: 239 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 53 insertions, 10 deletions

diff --git a/modutils/modutils.c b/modutils/modutils.c
index 969926db9..850a8683b 100644
--- 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;
 }