On 09/06/2012 04:13 AM, Hu Tao wrote:
> In many places we store bitmap info in a chunk of data
> (pointed to by a char *), and have redundant codes to
> set/unset bits. This patch extends virBitmap, and convert
> those codes to use virBitmap in subsequent patches.
> ---
>
> struct _virBitmap {
> - size_t size;
> - unsigned long *map;
> + size_t size; /* size in bits */
> + size_t size2; /* size in LONGs */
The name 'size2' isn't very descriptive. Maybe we should rename to
s/size/max_bit/ and s/size2/map_len/ for easier reading?
> + unsigned long *map; /* bits are stored in little-endian format */
This comment...
> +/* Helper function. caller must ensure b < bitmap->size */
> +static bool virBitmapIsSet(virBitmapPtr bitmap, size_t b)
> +{
> + return !!(bitmap->map[VIR_BITMAP_UNIT_OFFSET(b)] & VIR_BITMAP_BIT(b));
...and this code disagree. This code is reading in machine-native
format, not little-endian. And I much prefer operating in
machine-native format. Which means when converting from char* to long,
you'll have to properly pass things through endian conversion, rather
than requiring the longs to be little-endian.
> +char *virBitmapFormat(virBitmapPtr bitmap)
> +{
> + virBuffer buf = VIR_BUFFER_INITIALIZER;
> + int first = -1;
> + int start, cur;
> + int ret;
> + bool isset;
> +
> + if (!bitmap)
> + return NULL;
> +
> + cur = 0;
> + start = -1;
> + while (cur < bitmap->size) {
> + ret = virBitmapGetBit(bitmap, cur, &isset);
I'm wondering if we should optimize this by using things like ffsl() and
iterating a long at a time for longs that are 0 or -1, rather than
blindly processing one bit at a time. Or even make this use the new
virBitmapNextSetBit, and have that function be optimized a bit more.
> + if (ret != 0)
> + goto error;
> + else if (isset) {
Style. Since the else branch used {}, the if branch must also use {}.
> + if (start == -1)
> + start = cur;
> + } else if (start != -1) {
> + if (!first)
> + virBufferAddLit(&buf, ",");
> + else
> + first = 0;
> + if (cur == start + 1)
> + virBufferAsprintf(&buf, "%d", start);
> + else
> + virBufferAsprintf(&buf, "%d-%d", start, cur - 1);
> + start = -1;
> + }
> + cur++;
> + }
> +
> + if (start != -1) {
> + if (!first)
> + virBufferAddLit(&buf, ",");
> + if (cur == start + 1)
> + virBufferAsprintf(&buf, "%d", start);
> + else
> + virBufferAsprintf(&buf, "%d-%d", start, cur - 1);
> + }
> +
> + if (virBufferError(&buf)) {
> +error:
> + virBufferFreeAndReset(&buf);
> + return NULL;
> + }
> +
> + return virBufferContentAndReset(&buf);
Ouch. If the bitset is completely unset, then this returns NULL for
both errors and success. You need to special-case a map that is
completely unset to return strdup("") instead.
> +
> +#ifdef __BIG_ENDIAN__
> +static unsigned long
> +virSwapEndian(unsigned long l)
Yuck. __BIG_ENDIAN__ vs. __LITTLE_ENDIAN__ is not guaranteed to exist.
And even if you can rely on it, there's bound to be better ways to
implement this instead of open-coding it ourselves (not to mention that
by avoiding the #ifdefs, we avoid introducing bugs in the big-endian
code that cannot be detected on little-endian machines). (Hmm, too bad
gnulib doesn't guarantee be32toh and be64toh).
> +/**
> + * virBitmapAllocFromData:
> + * @data: the data
> + * @len: length of @data in bytes
> + *
> + * Allocate a bitmap from a chunk of data containing bits
> + * information
> + *
> + * Returns a pointer to the allocated bitmap or NULL if
> + * memory cannot be allocated.
> + */
> +virBitmapPtr virBitmapAllocFromData(void *data, int len)
> +{
> + virBitmapPtr bitmap;
> +#ifdef __BIG_ENDIAN__
> + int i;
> +#endif
> +
> + bitmap = virBitmapAlloc(len * CHAR_BIT);
> + if (!bitmap)
> + return NULL;
> +
> + memcpy(bitmap->map, data, len);
Instead of trying to memcpy() and then conditionally virSwapEndian(), I
would just do it the manual way of reading one byte at a time for both
endian types. Fewer #ifdefs, less ugly code.
> +int virBitmapToData(virBitmapPtr bitmap, char **data, int *dataLen)
> +{
> + int len;
> +#ifdef __BIG_ENDIAN__
> + unsigned long *l;
> +#endif
> +
> + len = bitmap->size2 * (VIR_BITMAP_BITS_PER_UNIT / CHAR_BIT);
> +
> + if (VIR_ALLOC_N(*data, len) < 0)
> + return -1;
> +
> + memcpy(*data, bitmap->map, len);
> + *dataLen = len;
> +
> +#ifdef __BIG_ENDIAN__
> + l = (unsigned long *)*data;
> + for (i = 0; i < bitmap->size2; i++, l++)
> + *l = virSwapEndian(*l);
> +#endif
Again, I'm not a fan of these #ifdefs.
> +int virBitmapNextSetBit(virBitmapPtr bitmap, int pos)
> +{
> + int nl;
> + int nb;
> + unsigned long bits;
> +
> + if (pos < 0)
> + pos = -1;
> +
> + pos++;
> +
> + if (pos >= bitmap->size)
> + return -1;
> +
> + nl = pos / VIR_BITMAP_BITS_PER_UNIT;
> + nb = pos % VIR_BITMAP_BITS_PER_UNIT;
> +
> + bits = bitmap->map[nl] & ~((1UL << nb) - 1);
> +
> + while (bits == 0 && ++nl < bitmap->size2) {
> + bits = bitmap->map[nl];
> + }
Use ffsl() instead of iterating one bit at a time.
> +
> + if (bits == 0)
> + return -1;
> +
> + return __builtin_ctzl(bits) + nl * VIR_BITMAP_BITS_PER_UNIT;
__builtin_ctzl() is not guaranteed to exist. ffsl() should already give
you what you need.
> +++ b/tests/virbitmaptest.c
> @@ -0,0 +1,233 @@
> +#include <config.h>
> +
> +#include <time.h>
> +#include <sched.h>
What are you using <time.h> and <sched.h> for?
It's late for me, so I didn't closely read the entire patch, so much as
identified things that jumped out on first glance.
--
Eric Blake eblake@xxxxxxxxxx +1-919-301-3266
Libvirt virtualization library http://libvirt.org
Attachment:
signature.asc
Description: OpenPGP digital signature
-- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list