[initrd] Swap initrds entirely in-place via triple reversal

Eliminate the requirement for free space when reshuffling initrds by
swapping adjacent initrds using an in-place triple reversal.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/image/initrd.c b/src/image/initrd.c
index 511f95f10c2fca29ea5f1da3c34d6ef730c99557..386414795a4836ea09a72e78155d29ec95b0e459 100644 (file)
--- a/src/image/initrd.c
+++ b/src/image/initrd.c
@@ -45,9 +45,8 @@ static physaddr_t initrd_top;
  * Squash initrds as high as possible in memory
  *
  * @v top              Highest possible physical address
- * @ret used           Lowest physical address used by initrds
  */
-static physaddr_t initrd_squash_high ( physaddr_t top ) {
+static void initrd_squash_high ( physaddr_t top ) {
        physaddr_t current = top;
        struct image *initrd;
        struct image *highest;
@@ -100,8 +99,25 @@ static physaddr_t initrd_squash_high ( physaddr_t top ) {
                        initrd->data = data;
                }
        }
+}
 
-       return current;
+/**
+ * Reverse aligned memory region
+ *
+ * @v data             Memory region
+ * @v len              Length of region
+ */
+static void initrd_reverse ( void *data, size_t len ) {
+       unsigned long *low = data;
+       unsigned long *high = ( data + len );
+       unsigned long tmp;
+
+       /* Reverse region */
+       for ( high-- ; low < high ; low++, high-- ) {
+               tmp = *low;
+               *low = *high;
+               *high = tmp;
+       }
 }
 
 /**
@@ -109,14 +125,12 @@ static physaddr_t initrd_squash_high ( physaddr_t top ) {
  *
  * @v low              Lower initrd
  * @v high             Higher initrd
- * @v free             Free space
- * @v free_len         Length of free space
  */
-static void initrd_swap ( struct image *low, struct image *high,
-                         void *free, size_t free_len ) {
-       size_t len = 0;
-       size_t frag_len;
-       size_t new_len;
+static void initrd_swap ( struct image *low, struct image *high ) {
+       size_t low_len;
+       size_t high_len;
+       size_t len;
+       void *data;
 
        DBGC ( &images, "INITRD swapping %s [%#08lx,%#08lx)<->[%#08lx,%#08lx) "
               "%s\n", low->name, virt_to_phys ( low->data ),
@@ -124,41 +138,30 @@ static void initrd_swap ( struct image *low, struct image *high,
               virt_to_phys ( high->data ),
               ( virt_to_phys ( high->data ) + high->len ), high->name );
 
-       /* Round down length of free space */
-       free_len &= ~( INITRD_ALIGN - 1 );
-       assert ( free_len > 0 );
-
-       /* Swap image data */
-       while ( len < high->len ) {
-
-               /* Calculate maximum fragment length */
-               frag_len = ( high->len - len );
-               if ( frag_len > free_len )
-                       frag_len = free_len;
-               new_len = ( ( len + frag_len + INITRD_ALIGN - 1 ) &
-                           ~( INITRD_ALIGN - 1 ) );
-
-               /* Swap fragments */
-               memcpy ( free, ( high->data + len ), frag_len );
-               memmove ( ( low->rwdata + new_len ), ( low->data + len ),
-                         low->len );
-               memcpy ( ( low->rwdata + len ), free, frag_len );
-               len = new_len;
-       }
+       /* Calculate padded lengths */
+       low_len = ( ( low->len + INITRD_ALIGN - 1 ) & ~( INITRD_ALIGN - 1 ) );
+       high_len = ( ( high->len + INITRD_ALIGN - 1 ) & ~( INITRD_ALIGN - 1 ));
+       len = ( low_len + high_len );
+       data = low->rwdata;
+       assert ( high->data == ( data + low_len ) );
 
        /* Adjust data pointers */
-       high->data = low->data;
-       low->data += len;
+       high->data -= low_len;
+       low->data += high_len;
+       assert ( high->data == data );
+
+       /* Swap content via triple reversal */
+       initrd_reverse ( data, len );
+       initrd_reverse ( low->rwdata, low_len );
+       initrd_reverse ( high->rwdata, high_len );
 }
 
 /**
  * Swap position of any two adjacent initrds not currently in the correct order
  *
- * @v free             Free space
- * @v free_len         Length of free space
  * @ret swapped                A pair of initrds was swapped
  */
-static int initrd_swap_any ( void *free, size_t free_len ) {
+static int initrd_swap_any ( void ) {
        struct image *low;
        struct image *high;
        const void *adjacent;
@@ -184,7 +187,7 @@ static int initrd_swap_any ( void *free, size_t free_len ) {
 
                        /* If we have found the adjacent image, swap and exit */
                        if ( high->data == adjacent ) {
-                               initrd_swap ( low, high, free, free_len );
+                               initrd_swap ( low, high );
                                return 1;
                        }
                }
@@ -228,9 +231,6 @@ static void initrd_dump ( void ) {
  */
 void initrd_reshuffle ( physaddr_t bottom ) {
        physaddr_t top;
-       physaddr_t used;
-       void *free;
-       size_t free_len;
 
        /* Calculate limits of available space for initrds */
        top = ( initrd_top ? initrd_top : uheap_end );
@@ -241,14 +241,10 @@ void initrd_reshuffle ( physaddr_t bottom ) {
        initrd_dump();
 
        /* Squash initrds as high as possible in memory */
-       used = initrd_squash_high ( top );
-
-       /* Calculate available free space */
-       free = phys_to_virt ( bottom );
-       free_len = ( used - bottom );
+       initrd_squash_high ( top );
 
        /* Bubble-sort initrds into desired order */
-       while ( initrd_swap_any ( free, free_len ) ) {}
+       while ( initrd_swap_any() ) {}
 
        /* Debug */
        initrd_dump();
@@ -270,9 +266,6 @@ int initrd_reshuffle_check ( size_t len, physaddr_t bottom ) {
        assert ( bottom >= uheap_limit );
        available = ( top - bottom );
 
-       /* Allow for a sensible minimum amount of free space */
-       len += INITRD_MIN_FREE_LEN;
-
        /* Check for available space */
        return ( ( len < available ) ? 0 : -ENOBUFS );
 }

diff --git a/src/include/ipxe/initrd.h b/src/include/ipxe/initrd.h
index 0d70b07319fcef48beac1c101d96c06ea50d88de..0b0ba0967942ce4895b2fe799bc497d7b1cf7411 100644 (file)
--- a/src/include/ipxe/initrd.h
+++ b/src/include/ipxe/initrd.h
@@ -11,12 +11,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <stdint.h>
 
-/** Minimum free space required to reshuffle initrds
- *
- * Chosen to avoid absurdly long reshuffling times
- */
-#define INITRD_MIN_FREE_LEN ( 512 * 1024 )
-
 extern void initrd_reshuffle ( physaddr_t bottom );
 extern int initrd_reshuffle_check ( size_t len, physaddr_t bottom );