kbuild: document howto build external modules using several directories

[linux-2.6/verdex.git] / drivers / block / rd.c

/*
 * ramdisk.c - Multiple RAM disk driver - gzip-loading version - v. 0.8 beta.
 *
 * (C) Chad Page, Theodore Ts'o, et. al, 1995.
 *
 * This RAM disk is designed to have filesystems created on it and mounted
 * just like a regular floppy disk.
 *
 * It also does something suggested by Linus: use the buffer cache as the
 * RAM disk data.  This makes it possible to dynamically allocate the RAM disk
 * buffer - with some consequences I have to deal with as I write this.
 *
 * This code is based on the original ramdisk.c, written mostly by
 * Theodore Ts'o (TYT) in 1991.  The code was largely rewritten by
 * Chad Page to use the buffer cache to store the RAM disk data in
 * 1995; Theodore then took over the driver again, and cleaned it up
 * for inclusion in the mainline kernel.
 *
 * The original CRAMDISK code was written by Richard Lyons, and
 * adapted by Chad Page to use the new RAM disk interface.  Theodore
 * Ts'o rewrote it so that both the compressed RAM disk loader and the
 * kernel decompressor uses the same inflate.c codebase.  The RAM disk
 * loader now also loads into a dynamic (buffer cache based) RAM disk,
 * not the old static RAM disk.  Support for the old static RAM disk has
 * been completely removed.
 *
 * Loadable module support added by Tom Dyas.
 *
 * Further cleanups by Chad Page (page0588@sundance.sjsu.edu):
 *      Cosmetic changes in #ifdef MODULE, code movement, etc.
 *      When the RAM disk module is removed, free the protected buffers
 *      Default RAM disk size changed to 2.88 MB
 *
 *  Added initrd: Werner Almesberger & Hans Lermen, Feb '96
 *
 * 4/25/96 : Made RAM disk size a parameter (default is now 4 MB)
 *              - Chad Page
 *
 * Add support for fs images split across >1 disk, Paul Gortmaker, Mar '98
 *
 * Make block size and block size shift for RAM disks a global macro
 * and set blk_size for -ENOSPC,     Werner Fink <werner@suse.de>, Apr '99
 */

#include <linux/config.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <asm/atomic.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/pagemap.h>
#include <linux/blkdev.h>
#include <linux/genhd.h>
#include <linux/buffer_head.h>          /* for invalidate_bdev() */
#include <linux/backing-dev.h>
#include <linux/blkpg.h>
#include <linux/writeback.h>

#include <asm/uaccess.h>

/* Various static variables go here.  Most are used only in the RAM disk code.
 */

static struct gendisk *rd_disks[CONFIG_BLK_DEV_RAM_COUNT];
static struct block_device *rd_bdev[CONFIG_BLK_DEV_RAM_COUNT];/* Protected device data */
static struct request_queue *rd_queue[CONFIG_BLK_DEV_RAM_COUNT];

/*
 * Parameters for the boot-loading of the RAM disk.  These are set by
 * init/main.c (from arguments to the kernel command line) or from the
 * architecture-specific setup routine (from the stored boot sector
 * information).
 */
int rd_size = CONFIG_BLK_DEV_RAM_SIZE;          /* Size of the RAM disks */
/*
 * It would be very desirable to have a soft-blocksize (that in the case
 * of the ramdisk driver is also the hardblocksize ;) of PAGE_SIZE because
 * doing that we'll achieve a far better MM footprint. Using a rd_blocksize of
 * BLOCK_SIZE in the worst case we'll make PAGE_SIZE/BLOCK_SIZE buffer-pages
 * unfreeable. With a rd_blocksize of PAGE_SIZE instead we are sure that only
 * 1 page will be protected. Depending on the size of the ramdisk you
 * may want to change the ramdisk blocksize to achieve a better or worse MM
 * behaviour. The default is still BLOCK_SIZE (needed by rd_load_image that
 * supposes the filesystem in the image uses a BLOCK_SIZE blocksize).
 */
static int rd_blocksize = BLOCK_SIZE;           /* blocksize of the RAM disks */

/*
 * Copyright (C) 2000 Linus Torvalds.
 *               2000 Transmeta Corp.
 * aops copied from ramfs.
 */

/*
 * If a ramdisk page has buffers, some may be uptodate and some may be not.
 * To bring the page uptodate we zero out the non-uptodate buffers.  The
 * page must be locked.
 */
static void make_page_uptodate(struct page *page)
{
        if (page_has_buffers(page)) {
                struct buffer_head *bh = page_buffers(page);
                struct buffer_head *head = bh;

                do {
                        if (!buffer_uptodate(bh)) {
                                memset(bh->b_data, 0, bh->b_size);
                                /*
                                 * akpm: I'm totally undecided about this.  The
                                 * buffer has just been magically brought "up to
                                 * date", but nobody should want to be reading
                                 * it anyway, because it hasn't been used for
                                 * anything yet.  It is still in a "not read
                                 * from disk yet" state.
                                 *
                                 * But non-uptodate buffers against an uptodate
                                 * page are against the rules.  So do it anyway.
                                 */
                                 set_buffer_uptodate(bh);
                        }
                } while ((bh = bh->b_this_page) != head);
        } else {
                memset(page_address(page), 0, PAGE_CACHE_SIZE);
        }
        flush_dcache_page(page);
        SetPageUptodate(page);
}

static int ramdisk_readpage(struct file *file, struct page *page)
{
        if (!PageUptodate(page))
                make_page_uptodate(page);
        unlock_page(page);
        return 0;
}

static int ramdisk_prepare_write(struct file *file, struct page *page,
                                unsigned offset, unsigned to)
{
        if (!PageUptodate(page))
                make_page_uptodate(page);
        return 0;
}

static int ramdisk_commit_write(struct file *file, struct page *page,
                                unsigned offset, unsigned to)
{
        set_page_dirty(page);
        return 0;
}

/*
 * ->writepage to the the blockdev's mapping has to redirty the page so that the
 * VM doesn't go and steal it.  We return AOP_WRITEPAGE_ACTIVATE so that the VM
 * won't try to (pointlessly) write the page again for a while.
 *
 * Really, these pages should not be on the LRU at all.
 */
static int ramdisk_writepage(struct page *page, struct writeback_control *wbc)
{
        if (!PageUptodate(page))
                make_page_uptodate(page);
        SetPageDirty(page);
        if (wbc->for_reclaim)
                return AOP_WRITEPAGE_ACTIVATE;
        unlock_page(page);
        return 0;
}

/*
 * This is a little speedup thing: short-circuit attempts to write back the
 * ramdisk blockdev inode to its non-existent backing store.
 */
static int ramdisk_writepages(struct address_space *mapping,
                                struct writeback_control *wbc)
{
        return 0;
}

/*
 * ramdisk blockdev pages have their own ->set_page_dirty() because we don't
 * want them to contribute to dirty memory accounting.
 */
static int ramdisk_set_page_dirty(struct page *page)
{
        SetPageDirty(page);
        return 0;
}

static struct address_space_operations ramdisk_aops = {
        .readpage       = ramdisk_readpage,
        .prepare_write  = ramdisk_prepare_write,
        .commit_write   = ramdisk_commit_write,
        .writepage      = ramdisk_writepage,
        .set_page_dirty = ramdisk_set_page_dirty,
        .writepages     = ramdisk_writepages,
};

static int rd_blkdev_pagecache_IO(int rw, struct bio_vec *vec, sector_t sector,
                                struct address_space *mapping)
{
        pgoff_t index = sector >> (PAGE_CACHE_SHIFT - 9);
        unsigned int vec_offset = vec->bv_offset;
        int offset = (sector << 9) & ~PAGE_CACHE_MASK;
        int size = vec->bv_len;
        int err = 0;

        do {
                int count;
                struct page *page;
                char *src;
                char *dst;

                count = PAGE_CACHE_SIZE - offset;
                if (count > size)
                        count = size;
                size -= count;

                page = grab_cache_page(mapping, index);
                if (!page) {
                        err = -ENOMEM;
                        goto out;
                }

                if (!PageUptodate(page))
                        make_page_uptodate(page);

                index++;

                if (rw == READ) {
                        src = kmap_atomic(page, KM_USER0) + offset;
                        dst = kmap_atomic(vec->bv_page, KM_USER1) + vec_offset;
                } else {
                        src = kmap_atomic(vec->bv_page, KM_USER0) + vec_offset;
                        dst = kmap_atomic(page, KM_USER1) + offset;
                }
                offset = 0;
                vec_offset += count;

                memcpy(dst, src, count);

                kunmap_atomic(src, KM_USER0);
                kunmap_atomic(dst, KM_USER1);

                if (rw == READ)
                        flush_dcache_page(vec->bv_page);
                else
                        set_page_dirty(page);
                unlock_page(page);
                put_page(page);
        } while (size);

 out:
        return err;
}

/*
 *  Basically, my strategy here is to set up a buffer-head which can't be
 *  deleted, and make that my Ramdisk.  If the request is outside of the
 *  allocated size, we must get rid of it...
 *
 * 19-JAN-1998  Richard Gooch <rgooch@atnf.csiro.au>  Added devfs support
 *
 */
static int rd_make_request(request_queue_t *q, struct bio *bio)
{
        struct block_device *bdev = bio->bi_bdev;
        struct address_space * mapping = bdev->bd_inode->i_mapping;
        sector_t sector = bio->bi_sector;
        unsigned long len = bio->bi_size >> 9;
        int rw = bio_data_dir(bio);
        struct bio_vec *bvec;
        int ret = 0, i;

        if (sector + len > get_capacity(bdev->bd_disk))
                goto fail;

        if (rw==READA)
                rw=READ;

        bio_for_each_segment(bvec, bio, i) {
                ret |= rd_blkdev_pagecache_IO(rw, bvec, sector, mapping);
                sector += bvec->bv_len >> 9;
        }
        if (ret)
                goto fail;

        bio_endio(bio, bio->bi_size, 0);
        return 0;
fail:
        bio_io_error(bio, bio->bi_size);
        return 0;
} 

static int rd_ioctl(struct inode *inode, struct file *file,
                        unsigned int cmd, unsigned long arg)
{
        int error;
        struct block_device *bdev = inode->i_bdev;

        if (cmd != BLKFLSBUF)
                return -ENOTTY;

        /*
         * special: we want to release the ramdisk memory, it's not like with
         * the other blockdevices where this ioctl only flushes away the buffer
         * cache
         */
        error = -EBUSY;
        down(&bdev->bd_sem);
        if (bdev->bd_openers <= 2) {
                truncate_inode_pages(bdev->bd_inode->i_mapping, 0);
                error = 0;
        }
        up(&bdev->bd_sem);
        return error;
}

/*
 * This is the backing_dev_info for the blockdev inode itself.  It doesn't need
 * writeback and it does not contribute to dirty memory accounting.
 */
static struct backing_dev_info rd_backing_dev_info = {
        .ra_pages       = 0,    /* No readahead */
        .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK | BDI_CAP_MAP_COPY,
        .unplug_io_fn   = default_unplug_io_fn,
};

/*
 * This is the backing_dev_info for the files which live atop the ramdisk
 * "device".  These files do need writeback and they do contribute to dirty
 * memory accounting.
 */
static struct backing_dev_info rd_file_backing_dev_info = {
        .ra_pages       = 0,    /* No readahead */
        .capabilities   = BDI_CAP_MAP_COPY,     /* Does contribute to dirty memory */
        .unplug_io_fn   = default_unplug_io_fn,
};

static int rd_open(struct inode *inode, struct file *filp)
{
        unsigned unit = iminor(inode);

        if (rd_bdev[unit] == NULL) {
                struct block_device *bdev = inode->i_bdev;
                struct address_space *mapping;
                unsigned bsize;
                gfp_t gfp_mask;

                inode = igrab(bdev->bd_inode);
                rd_bdev[unit] = bdev;
                bdev->bd_openers++;
                bsize = bdev_hardsect_size(bdev);
                bdev->bd_block_size = bsize;
                inode->i_blkbits = blksize_bits(bsize);
                inode->i_size = get_capacity(bdev->bd_disk)<<9;

                mapping = inode->i_mapping;
                mapping->a_ops = &ramdisk_aops;
                mapping->backing_dev_info = &rd_backing_dev_info;
                bdev->bd_inode_backing_dev_info = &rd_file_backing_dev_info;

                /*
                 * Deep badness.  rd_blkdev_pagecache_IO() needs to allocate
                 * pagecache pages within a request_fn.  We cannot recur back
                 * into the filesytem which is mounted atop the ramdisk, because
                 * that would deadlock on fs locks.  And we really don't want
                 * to reenter rd_blkdev_pagecache_IO when we're already within
                 * that function.
                 *
                 * So we turn off __GFP_FS and __GFP_IO.
                 *
                 * And to give this thing a hope of working, turn on __GFP_HIGH.
                 * Hopefully, there's enough regular memory allocation going on
                 * for the page allocator emergency pools to keep the ramdisk
                 * driver happy.
                 */
                gfp_mask = mapping_gfp_mask(mapping);
                gfp_mask &= ~(__GFP_FS|__GFP_IO);
                gfp_mask |= __GFP_HIGH;
                mapping_set_gfp_mask(mapping, gfp_mask);
        }

        return 0;
}

static struct block_device_operations rd_bd_op = {
        .owner =        THIS_MODULE,
        .open =         rd_open,
        .ioctl =        rd_ioctl,
};

/*
 * Before freeing the module, invalidate all of the protected buffers!
 */
static void __exit rd_cleanup(void)
{
        int i;

        for (i = 0; i < CONFIG_BLK_DEV_RAM_COUNT; i++) {
                struct block_device *bdev = rd_bdev[i];
                rd_bdev[i] = NULL;
                if (bdev) {
                        invalidate_bdev(bdev, 1);
                        blkdev_put(bdev);
                }
                del_gendisk(rd_disks[i]);
                put_disk(rd_disks[i]);
                blk_cleanup_queue(rd_queue[i]);
        }
        devfs_remove("rd");
        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
}

/*
 * This is the registration and initialization section of the RAM disk driver
 */
static int __init rd_init(void)
{
        int i;
        int err = -ENOMEM;

        if (rd_blocksize > PAGE_SIZE || rd_blocksize < 512 ||
                        (rd_blocksize & (rd_blocksize-1))) {
                printk("RAMDISK: wrong blocksize %d, reverting to defaults\n",
                       rd_blocksize);
                rd_blocksize = BLOCK_SIZE;
        }

        for (i = 0; i < CONFIG_BLK_DEV_RAM_COUNT; i++) {
                rd_disks[i] = alloc_disk(1);
                if (!rd_disks[i])
                        goto out;
        }

        if (register_blkdev(RAMDISK_MAJOR, "ramdisk")) {
                err = -EIO;
                goto out;
        }

        devfs_mk_dir("rd");

        for (i = 0; i < CONFIG_BLK_DEV_RAM_COUNT; i++) {
                struct gendisk *disk = rd_disks[i];

                rd_queue[i] = blk_alloc_queue(GFP_KERNEL);
                if (!rd_queue[i])
                        goto out_queue;

                blk_queue_make_request(rd_queue[i], &rd_make_request);
                blk_queue_hardsect_size(rd_queue[i], rd_blocksize);

                /* rd_size is given in kB */
                disk->major = RAMDISK_MAJOR;
                disk->first_minor = i;
                disk->fops = &rd_bd_op;
                disk->queue = rd_queue[i];
                disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
                sprintf(disk->disk_name, "ram%d", i);
                sprintf(disk->devfs_name, "rd/%d", i);
                set_capacity(disk, rd_size * 2);
                add_disk(rd_disks[i]);
        }

        /* rd_size is given in kB */
        printk("RAMDISK driver initialized: "
                "%d RAM disks of %dK size %d blocksize\n",
                CONFIG_BLK_DEV_RAM_COUNT, rd_size, rd_blocksize);

        return 0;
out_queue:
        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
out:
        while (i--) {
                put_disk(rd_disks[i]);
                blk_cleanup_queue(rd_queue[i]);
        }
        return err;
}

module_init(rd_init);
module_exit(rd_cleanup);

/* options - nonmodular */
#ifndef MODULE
static int __init ramdisk_size(char *str)
{
        rd_size = simple_strtol(str,NULL,0);
        return 1;
}
static int __init ramdisk_size2(char *str)      /* kludge */
{
        return ramdisk_size(str);
}
static int __init ramdisk_blocksize(char *str)
{
        rd_blocksize = simple_strtol(str,NULL,0);
        return 1;
}
__setup("ramdisk=", ramdisk_size);
__setup("ramdisk_size=", ramdisk_size2);
__setup("ramdisk_blocksize=", ramdisk_blocksize);
#endif

/* options - modular */
module_param(rd_size, int, 0);
MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
module_param(rd_blocksize, int, 0);
MODULE_PARM_DESC(rd_blocksize, "Blocksize of each RAM disk in bytes.");
MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);

MODULE_LICENSE("GPL");