dev_bdev.c

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/*
 * fs/logfs/dev_bdev.c  - Device access methods for block devices
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <[email protected]>
 */
#include "logfs.h"
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/gfp.h>
#include <linux/prefetch.h>

#define PAGE_OFS(ofs) ((ofs) & (PAGE_SIZE-1))

static void request_complete(struct bio *bio, int err)
{
    complete((struct completion *)bio->bi_private);
}

static int sync_request(struct page *page, struct block_device *bdev, int rw)
{
    struct bio bio;
    struct bio_vec bio_vec;
    struct completion complete;

    bio_init(&bio);
    bio.bi_max_vecs = 1;
    bio.bi_io_vec = &bio_vec;
    bio_vec.bv_page = page;
    bio_vec.bv_len = PAGE_SIZE;
    bio_vec.bv_offset = 0;
    bio.bi_vcnt = 1;
    bio.bi_idx = 0;
    bio.bi_size = PAGE_SIZE;
    bio.bi_bdev = bdev;
    bio.bi_sector = page->index * (PAGE_SIZE >> 9);
    init_completion(&complete);
    bio.bi_private = &complete;
    bio.bi_end_io = request_complete;

    submit_bio(rw, &bio);
    wait_for_completion(&complete);
    return test_bit(BIO_UPTODATE, &bio.bi_flags) ? 0 : -EIO;
}

static int bdev_readpage(void *_sb, struct page *page)
{
    struct super_block *sb = _sb;
    struct block_device *bdev = logfs_super(sb)->s_bdev;
    int err;

    err = sync_request(page, bdev, READ);
    if (err) {
        ClearPageUptodate(page);
        SetPageError(page);
    } else {
        SetPageUptodate(page);
        ClearPageError(page);
    }
    unlock_page(page);
    return err;
}

static DECLARE_WAIT_QUEUE_HEAD(wq);

static void writeseg_end_io(struct bio *bio, int err)
{
    const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
    struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
    struct super_block *sb = bio->bi_private;
    struct logfs_super *super = logfs_super(sb);
    struct page *page;

    BUG_ON(!uptodate); /* FIXME: Retry io or write elsewhere */
    BUG_ON(err);
    BUG_ON(bio->bi_vcnt == 0);
    do {
        page = bvec->bv_page;
        if (--bvec >= bio->bi_io_vec)
            prefetchw(&bvec->bv_page->flags);

        end_page_writeback(page);
        page_cache_release(page);
    } while (bvec >= bio->bi_io_vec);
    bio_put(bio);
    if (atomic_dec_and_test(&super->s_pending_writes))
        wake_up(&wq);
}

static int __bdev_writeseg(struct super_block *sb, u64 ofs, pgoff_t index,
        size_t nr_pages)
{
    struct logfs_super *super = logfs_super(sb);
    struct address_space *mapping = super->s_mapping_inode->i_mapping;
    struct bio *bio;
    struct page *page;
    unsigned int max_pages;
    int i;

    max_pages = min(nr_pages, (size_t) bio_get_nr_vecs(super->s_bdev));

    bio = bio_alloc(GFP_NOFS, max_pages);
    BUG_ON(!bio);

    for (i = 0; i < nr_pages; i++) {
        if (i >= max_pages) {
            /* Block layer cannot split bios :( */
            bio->bi_vcnt = i;
            bio->bi_idx = 0;
            bio->bi_size = i * PAGE_SIZE;
            bio->bi_bdev = super->s_bdev;
            bio->bi_sector = ofs >> 9;
            bio->bi_private = sb;
            bio->bi_end_io = writeseg_end_io;
            atomic_inc(&super->s_pending_writes);
            submit_bio(WRITE, bio);

            ofs += i * PAGE_SIZE;
            index += i;
            nr_pages -= i;
            i = 0;

            bio = bio_alloc(GFP_NOFS, max_pages);
            BUG_ON(!bio);
        }
        page = find_lock_page(mapping, index + i);
        BUG_ON(!page);
        bio->bi_io_vec[i].bv_page = page;
        bio->bi_io_vec[i].bv_len = PAGE_SIZE;
        bio->bi_io_vec[i].bv_offset = 0;

        BUG_ON(PageWriteback(page));
        set_page_writeback(page);
        unlock_page(page);
    }
    bio->bi_vcnt = nr_pages;
    bio->bi_idx = 0;
    bio->bi_size = nr_pages * PAGE_SIZE;
    bio->bi_bdev = super->s_bdev;
    bio->bi_sector = ofs >> 9;
    bio->bi_private = sb;
    bio->bi_end_io = writeseg_end_io;
    atomic_inc(&super->s_pending_writes);
    submit_bio(WRITE, bio);
    return 0;
}

static void bdev_writeseg(struct super_block *sb, u64 ofs, size_t len)
{
    struct logfs_super *super = logfs_super(sb);
    int head;

    BUG_ON(super->s_flags & LOGFS_SB_FLAG_RO);

    if (len == 0) {
        /* This can happen when the object fit perfectly into a
         * segment, the segment gets written per sync and subsequently
         * closed.
         */
        return;
    }
    head = ofs & (PAGE_SIZE - 1);
    if (head) {
        ofs -= head;
        len += head;
    }
    len = PAGE_ALIGN(len);
    __bdev_writeseg(sb, ofs, ofs >> PAGE_SHIFT, len >> PAGE_SHIFT);
}


static void erase_end_io(struct bio *bio, int err) 
{ 
    const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); 
    struct super_block *sb = bio->bi_private; 
    struct logfs_super *super = logfs_super(sb); 

    BUG_ON(!uptodate); /* FIXME: Retry io or write elsewhere */ 
    BUG_ON(err); 
    BUG_ON(bio->bi_vcnt == 0); 
    bio_put(bio); 
    if (atomic_dec_and_test(&super->s_pending_writes))
        wake_up(&wq); 
} 

static int do_erase(struct super_block *sb, u64 ofs, pgoff_t index,
        size_t nr_pages)
{
    struct logfs_super *super = logfs_super(sb);
    struct bio *bio;
    unsigned int max_pages;
    int i;

    max_pages = min(nr_pages, (size_t) bio_get_nr_vecs(super->s_bdev));

    bio = bio_alloc(GFP_NOFS, max_pages);
    BUG_ON(!bio);

    for (i = 0; i < nr_pages; i++) {
        if (i >= max_pages) {
            /* Block layer cannot split bios :( */
            bio->bi_vcnt = i;
            bio->bi_idx = 0;
            bio->bi_size = i * PAGE_SIZE;
            bio->bi_bdev = super->s_bdev;
            bio->bi_sector = ofs >> 9;
            bio->bi_private = sb;
            bio->bi_end_io = erase_end_io;
            atomic_inc(&super->s_pending_writes);
            submit_bio(WRITE, bio);

            ofs += i * PAGE_SIZE;
            index += i;
            nr_pages -= i;
            i = 0;

            bio = bio_alloc(GFP_NOFS, max_pages);
            BUG_ON(!bio);
        }
        bio->bi_io_vec[i].bv_page = super->s_erase_page;
        bio->bi_io_vec[i].bv_len = PAGE_SIZE;
        bio->bi_io_vec[i].bv_offset = 0;
    }
    bio->bi_vcnt = nr_pages;
    bio->bi_idx = 0;
    bio->bi_size = nr_pages * PAGE_SIZE;
    bio->bi_bdev = super->s_bdev;
    bio->bi_sector = ofs >> 9;
    bio->bi_private = sb;
    bio->bi_end_io = erase_end_io;
    atomic_inc(&super->s_pending_writes);
    submit_bio(WRITE, bio);
    return 0;
}

static int bdev_erase(struct super_block *sb, loff_t to, size_t len,
        int ensure_write)
{
    struct logfs_super *super = logfs_super(sb);

    BUG_ON(to & (PAGE_SIZE - 1));
    BUG_ON(len & (PAGE_SIZE - 1));

    if (super->s_flags & LOGFS_SB_FLAG_RO)
        return -EROFS;

    if (ensure_write) {
        /*
         * Object store doesn't care whether erases happen or not.
         * But for the journal they are required.  Otherwise a scan
         * can find an old commit entry and assume it is the current
         * one, travelling back in time.
         */
        do_erase(sb, to, to >> PAGE_SHIFT, len >> PAGE_SHIFT);
    }

    return 0;
}

static void bdev_sync(struct super_block *sb)
{
    struct logfs_super *super = logfs_super(sb);

    wait_event(wq, atomic_read(&super->s_pending_writes) == 0);
}

static struct page *bdev_find_first_sb(struct super_block *sb, u64 *ofs)
{
    struct logfs_super *super = logfs_super(sb);
    struct address_space *mapping = super->s_mapping_inode->i_mapping;
    filler_t *filler = bdev_readpage;

    *ofs = 0;
    return read_cache_page(mapping, 0, filler, sb);
}

static struct page *bdev_find_last_sb(struct super_block *sb, u64 *ofs)
{
    struct logfs_super *super = logfs_super(sb);
    struct address_space *mapping = super->s_mapping_inode->i_mapping;
    filler_t *filler = bdev_readpage;
    u64 pos = (super->s_bdev->bd_inode->i_size & ~0xfffULL) - 0x1000;
    pgoff_t index = pos >> PAGE_SHIFT;

    *ofs = pos;
    return read_cache_page(mapping, index, filler, sb);
}

static int bdev_write_sb(struct super_block *sb, struct page *page)
{
    struct block_device *bdev = logfs_super(sb)->s_bdev;

    /* Nothing special to do for block devices. */
    return sync_request(page, bdev, WRITE);
}

static void bdev_put_device(struct logfs_super *s)
{
    blkdev_put(s->s_bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
}

static int bdev_can_write_buf(struct super_block *sb, u64 ofs)
{
    return 0;
}

static const struct logfs_device_ops bd_devops = {
    .find_first_sb  = bdev_find_first_sb,
    .find_last_sb   = bdev_find_last_sb,
    .write_sb   = bdev_write_sb,
    .readpage   = bdev_readpage,
    .writeseg   = bdev_writeseg,
    .erase      = bdev_erase,
    .can_write_buf  = bdev_can_write_buf,
    .sync       = bdev_sync,
    .put_device = bdev_put_device,
};

int logfs_get_sb_bdev(struct logfs_super *p, struct file_system_type *type,
        const char *devname)
{
    struct block_device *bdev;

    bdev = blkdev_get_by_path(devname, FMODE_READ|FMODE_WRITE|FMODE_EXCL,
                  type);
    if (IS_ERR(bdev))
        return PTR_ERR(bdev);

    if (MAJOR(bdev->bd_dev) == MTD_BLOCK_MAJOR) {
        int mtdnr = MINOR(bdev->bd_dev);
        blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
        return logfs_get_sb_mtd(p, mtdnr);
    }

    p->s_bdev = bdev;
    p->s_mtd = NULL;
    p->s_devops = &bd_devops;
    return 0;
}