@@ -40,21 +40,6 @@
* for the best explanations of this ordering.
*/
-/*
- * If a bitmap has a number of bits which is not a multiple of 8 then
- * the last few bits of the last byte of the bitmap can be
- * unexpectedly set which can confuse consumers (e.g. in the tools)
- * who also round up their loops to 8 bits. Ensure we clear those left
- * over bits so as to prevent surprises.
- */
-static void clamp_last_byte(uint8_t *bp, unsigned int nbits)
-{
- unsigned int remainder = nbits % 8;
-
- if (remainder)
- bp[nbits/8] &= (1U << remainder) - 1;
-}
-
int __bitmap_empty(const unsigned long *bitmap, unsigned int bits)
{
int k, lim = bits/BITS_PER_LONG;
@@ -338,7 +323,6 @@ static void bitmap_long_to_byte(uint8_t *bp, const unsigned long *lp,
nbits -= 8;
}
}
- clamp_last_byte(bp, nbits);
}
static void bitmap_byte_to_long(unsigned long *lp, const uint8_t *bp,
@@ -363,7 +347,6 @@ static void bitmap_long_to_byte(uint8_t *bp, const unsigned long *lp,
unsigned int nbits)
{
memcpy(bp, lp, DIV_ROUND_UP(nbits, BITS_PER_BYTE));
- clamp_last_byte(bp, nbits);
}
static void bitmap_byte_to_long(unsigned long *lp, const uint8_t *bp,
@@ -377,6 +360,13 @@ static void bitmap_byte_to_long(unsigned long *lp, const uint8_t *bp,
#endif
+/*
+ * If a bitmap has a number of bits which is not a multiple of 8 then
+ * the last few bits of the last byte of the bitmap can be
+ * unexpectedly set which can confuse consumers (e.g. in the tools)
+ * who also round up their loops to 8 bits. Ensure we clear those left
+ * over bits so as to prevent surprises.
+ */
int bitmap_to_xenctl_bitmap(struct xenctl_bitmap *xenctl_bitmap,
const unsigned long *bitmap, unsigned int nbits)
{
@@ -384,21 +374,43 @@ int bitmap_to_xenctl_bitmap(struct xenctl_bitmap *xenctl_bitmap,
uint8_t zero = 0;
int err = 0;
unsigned int xen_bytes = DIV_ROUND_UP(nbits, BITS_PER_BYTE);
- uint8_t *bytemap = xmalloc_array(uint8_t, xen_bytes);
-
- if ( !bytemap )
- return -ENOMEM;
+ uint8_t last;
guest_bytes = DIV_ROUND_UP(xenctl_bitmap->nr_bits, BITS_PER_BYTE);
copy_bytes = min(guest_bytes, xen_bytes);
- bitmap_long_to_byte(bytemap, bitmap, nbits);
+ if ( IS_ENABLED(__BIG_ENDIAN) )
+ {
+ uint8_t *bytemap = xmalloc_array(uint8_t, xen_bytes);
- if ( copy_bytes &&
- copy_to_guest(xenctl_bitmap->bitmap, bytemap, copy_bytes) )
- err = -EFAULT;
+ if ( !bytemap )
+ return -ENOMEM;
- xfree(bytemap);
+ bitmap_long_to_byte(bytemap, bitmap, nbits);
+ last = bytemap[nbits / 8];
+
+ if ( copy_bytes > 1 &&
+ copy_to_guest(xenctl_bitmap->bitmap, bytemap, copy_bytes - 1) )
+ err = -EFAULT;
+
+ xfree(bytemap);
+ }
+ else
+ {
+ const uint8_t *bytemap = (const uint8_t *)bitmap;
+ last = bytemap[nbits / 8];
+
+ if ( copy_bytes > 1 &&
+ copy_to_guest(xenctl_bitmap->bitmap, bytemap, copy_bytes - 1) )
+ err = -EFAULT;
+ }
+
+ if ( nbits % 8 )
+ last &= (1U << (nbits % 8)) - 1;
+
+ if ( copy_bytes > 0 &&
+ copy_to_guest_offset(xenctl_bitmap->bitmap, copy_bytes - 1, &last, 1) )
+ err = -EFAULT;
for ( i = copy_bytes; !err && i < guest_bytes; i++ )
if ( copy_to_guest_offset(xenctl_bitmap->bitmap, i, &zero, 1) )
The little endian implementation of bitmap_to_xenctl_bitmap leads to unnecessary xmallocs and xfrees. Given that Xen only supports little endian architectures, it is worth optimizing. This patch removes the need for the xmalloc on little endian architectures. Remove clamp_last_byte as it is only called once and only needs to modify one byte. Inline it. Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com> --- Changes in v4: - improve commit message - remove clamp_last_byte --- xen/common/bitmap.c | 64 +++++++++++++++++++++++++++------------------ 1 file changed, 38 insertions(+), 26 deletions(-)