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[Qemu-devel] questions about AIO Bitmap


From: Yaodong Yang
Subject: [Qemu-devel] questions about AIO Bitmap
Date: Fri, 16 Aug 2013 13:39:15 +0000 (GMT)

Hello everyone,

in QEMU 1.5.1, block-migration.c, there is a function below:

static void alloc_aio_bitmap(BlkMigDevState *bmds)
{
    BlockDriverState *bs = bmds->bs;
    int64_t bitmap_size;

    bitmap_size = (bdrv_getlength(bs) >> BDRV_SECTOR_BITS) +
            BDRV_SECTORS_PER_DIRTY_CHUNK * 8 - 1;
    bitmap_size /= BDRV_SECTORS_PER_DIRTY_CHUNK * 8;

    bmds->aio_bitmap = g_malloc0(bitmap_size);
}

I do not understand the calculation for the bitmap_size. Could someone explain it for me? 

Also, what's the difference between aio_bitmap and dirty_bitmap? How to calculate the size for dirty_bitmap?

Thanks!

Yaodong

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