On Mon, Nov 09, 2009 at 08:58:32PM +0100, Andries E. Brouwer wrote:
> static size_t
> read_lba(struct block_device *bdev, u64 lba, u8 * buffer, size_t count)
> {
> size_t totalreadcount = 0;
> sector_t n = lba * (bdev_logical_block_size(bdev) / 512);
>
> if (!bdev || !buffer || lba > last_lba(bdev))
> return 0;
>
> while (count) {
> int copied = 512;
> Sector sect;
> unsigned char *data = read_dev_sector(bdev, n++, §);
> if (!data)
> break;
> if (copied > count)
> copied = count;
> memcpy(buffer, data, copied);
> put_dev_sector(sect);
> buffer += copied;
> totalreadcount +=copied;
> count -= copied;
> }
> return totalreadcount;
> }
>
> Ugly - it looks as if you call read_dev_sector 8 times and each time
Yes, the function is really not elegant, but it follows the way how
all fs/partitions code reads sectors from disks.
> do a put_dev_sector afterwards to forget it again. Doesnt that mean
> that in order to read a 4096-byte sector the kernel goes to the hardware
> 8 times?
read_dev_sector() works with 512-byte sectors and it's interface to
read_mapping_page() which works with pages from cache.
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
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