ra_pages and max_sectors

["Philipp Kohlbecher" <xt28@gmx.de>]

Hello!

I was wondering why I can change the read-ahead size of my DVD drive via hdparm -a [size], but not by writing into /sys/block/hdb/queue/read_ahead_kb.

In other words: Why does queue_ra_store() [block/ll_rw_blk.c:3755] perform the following check

        if (ra_kb > (q->max_sectors >> 1))
                ra_kb = (q->max_sectors >> 1);

while blkdev_locked_ioctl() [block/ioctl.c:138] does not check this in the case that cmd == BLKRASET?

Thanks for your consideration,
- Philipp Kohlbecher


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