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Date: Wed, 8 May 2002 22:48:10 +0200
From: Pavel Machek <pavel@ucw.cz>
To: kernel list <linux-kernel@vger.kernel.org>
Subject: Reading page from given block device
Message-ID: <20020508204809.GA2300@elf.ucw.cz>
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Hi!

For swsusp, I kind of need to read 4K from given block device.

Here's my attempt:

static int bdev_read_page(kdev_t dev, long pos, void *buf)
{
        struct buffer_head *bh;
        struct block_device *bdev;

        if (pos%PAGE_SIZE) panic("Sorry, dave, I can't let you do
that!\n");
        bdev = bdget(kdev_t_to_nr(dev));
        if (!bdev) {
                printk("No block device for %s\n", __bdevname(dev));
                BUG();
        }
        printk("C");
        bh = __bread(bdev, pos/PAGE_SIZE, PAGE_SIZE);
        printk("D");
        bdput(bdev);
        if (!bh || (!bh->b_data)) {
                return -1;
        }
        memcpy(buf, bh->b_data, PAGE_SIZE);
        bforget(bh);                    /* FIXME: maybe bforget should
be here */
        return 0;
}

It works *once*, second time it deadlocks in __bread(). I tried both
bforget() and brelse(). Kernel is 2.5.13. What am I doing wrong/what's
wrong?

									Pavel
-- 
(about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa