On Fri, 24 Oct 2014 17:20:39 -0400 Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx> wrote:
> This is practically generic code; other filesystems will want to call
> it from other places, but there's nothing ext2-specific about it.
>
> Make it a little more generic by allowing it to take a count of the number
> of bytes to zero rather than fixing it to a single page. Thanks to Dave
> Hansen for suggesting that I need to call cond_resched() if zeroing more
> than one page.
>
> ...
>
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -20,8 +20,45 @@
> #include <linux/fs.h>
> #include <linux/genhd.h>
> #include <linux/mutex.h>
> +#include <linux/sched.h>
> #include <linux/uio.h>
>
> +int dax_clear_blocks(struct inode *inode, sector_t block, long size)
> +{
> + struct block_device *bdev = inode->i_sb->s_bdev;
> + sector_t sector = block << (inode->i_blkbits - 9);
> +
> + might_sleep();
> + do {
> + void *addr;
> + unsigned long pfn;
> + long count;
> +
> + count = bdev_direct_access(bdev, sector, &addr, &pfn, size);
> + if (count < 0)
> + return count;
> + BUG_ON(size < count);
> + while (count > 0) {
> + unsigned pgsz = PAGE_SIZE - offset_in_page(addr);
> + if (pgsz > count)
> + pgsz = count;
> + if (pgsz < PAGE_SIZE)
> + memset(addr, 0, pgsz);
> + else
> + clear_page(addr);
Are there any cache issues in all this code? flush_dcache_page(addr)?
> + addr += pgsz;
> + size -= pgsz;
> + count -= pgsz;
> + BUG_ON(pgsz & 511);
> + sector += pgsz / 512;
> + cond_resched();
> + }
> + } while (size);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(dax_clear_blocks);
>
> ...
>
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