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>

diff --git a/modutils/Config.in b/modutils/Config.in
index d2a2e04..83c12b6 100644 (file)
--- a/modutils/Config.in
+++ b/modutils/Config.in
@@ -121,6 +121,22 @@ config FEATURE_2_4_MODULES
          This increases size considerably. Say N unless you plan
          to run ancient kernels.
 
+config FEATURE_INSMOD_TRY_MMAP
+       bool "Try to load module from a mmap'ed area"
+       default n
+       depends on INSMOD || MODPROBE_SMALL
+       help
+         This option causes module loading code to try to mmap
+         module first. If it does not work (for example,
+         it does not work for compressed modules), module will be read
+         (and unpacked if needed) into a memory block allocated by malloc.
+
+         The only case when mmap works but malloc does not is when
+         you are trying to load a big module on a very memory-constrained
+         machine. Malloc will momentarily need 2x as much memory as mmap.
+
+         Choosing N saves about 250 bytes of code (on 32-bit x86).
+
 config FEATURE_INSMOD_VERSION_CHECKING
        bool "Enable module version checking"
        default n

diff --git a/modutils/modutils-24.c b/modutils/modutils-24.c
index e5ff54d..a878e74 100644 (file)
--- a/modutils/modutils-24.c
+++ b/modutils/modutils-24.c
@@ -3783,12 +3783,20 @@ int FAST_FUNC bb_init_module_24(const char *m_filename, const char *options)
        int m_has_modinfo;
 #endif
        char *image;
-       size_t image_size = 64 * 1024 * 1024;
-
-       /* Load module into memory and unzip if compressed */
-       image = xmalloc_open_zipped_read_close(m_filename, &image_size);
-       if (!image)
-               return EXIT_FAILURE;
+       size_t image_size;
+       bool mmaped;
+
+       image_size = INT_MAX - 4095;
+       mmaped = 0;
+       image = try_to_mmap_module(m_filename, &image_size);
+       if (image) {
+               mmaped = 1;
+       } else {
+               /* Load module into memory and unzip if compressed */
+               image = xmalloc_open_zipped_read_close(m_filename, &image_size);
+               if (!image)
+                       return EXIT_FAILURE;
+       }
 
        m_name = xstrdup(bb_basename(m_filename));
        /* "module.o[.gz]" -> "module" */
@@ -3901,7 +3909,10 @@ int FAST_FUNC bb_init_module_24(const char *m_filename, const char *options)
        exit_status = EXIT_SUCCESS;
 
  out:
-       free(image);
+       if (mmaped)
+               munmap(image, image_size);
+       else
+               free(image);
        free(m_name);
 
        return exit_status;

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;
 }
 

diff --git a/modutils/modutils.h b/modutils/modutils.h
index 1cf4bba..131a508 100644 (file)
--- a/modutils/modutils.h
+++ b/modutils/modutils.h
@@ -51,6 +51,12 @@ enum {
 #endif
 };
 
+#if ENABLE_FEATURE_INSMOD_TRY_MMAP
+void* FAST_FUNC try_to_mmap_module(const char *filename, size_t *image_size_p);
+#else
+# define try_to_mmap_module(filename, image_size) NULL
+#endif
+
 /* Return:
  * 0 on success,
  * -errno on open/read error,