dev_mtd.c

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/*
 * fs/logfs/dev_mtd.c   - Device access methods for MTD
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <[email protected]>
 */
#include "logfs.h"
#include <linux/completion.h>
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/slab.h>

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

static int logfs_mtd_read(struct super_block *sb, loff_t ofs, size_t len,
            void *buf)
{
    struct mtd_info *mtd = logfs_super(sb)->s_mtd;
    size_t retlen;
    int ret;

    ret = mtd_read(mtd, ofs, len, &retlen, buf);
    BUG_ON(ret == -EINVAL);
    if (ret)
        return ret;

    /* Not sure if we should loop instead. */
    if (retlen != len)
        return -EIO;

    return 0;
}

static int loffs_mtd_write(struct super_block *sb, loff_t ofs, size_t len,
            void *buf)
{
    struct logfs_super *super = logfs_super(sb);
    struct mtd_info *mtd = super->s_mtd;
    size_t retlen;
    loff_t page_start, page_end;
    int ret;

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

    BUG_ON((ofs >= mtd->size) || (len > mtd->size - ofs));
    BUG_ON(ofs != (ofs >> super->s_writeshift) << super->s_writeshift);
    BUG_ON(len > PAGE_CACHE_SIZE);
    page_start = ofs & PAGE_CACHE_MASK;
    page_end = PAGE_CACHE_ALIGN(ofs + len) - 1;
    ret = mtd_write(mtd, ofs, len, &retlen, buf);
    if (ret || (retlen != len))
        return -EIO;

    return 0;
}

/*
 * For as long as I can remember (since about 2001) mtd->erase has been an
 * asynchronous interface lacking the first driver to actually use the
 * asynchronous properties.  So just to prevent the first implementor of such
 * a thing from breaking logfs in 2350, we do the usual pointless dance to
 * declare a completion variable and wait for completion before returning
 * from logfs_mtd_erase().  What an exercise in futility!
 */
static void logfs_erase_callback(struct erase_info *ei)
{
    complete((struct completion *)ei->priv);
}

static int logfs_mtd_erase_mapping(struct super_block *sb, loff_t ofs,
                size_t len)
{
    struct logfs_super *super = logfs_super(sb);
    struct address_space *mapping = super->s_mapping_inode->i_mapping;
    struct page *page;
    pgoff_t index = ofs >> PAGE_SHIFT;

    for (index = ofs >> PAGE_SHIFT; index < (ofs + len) >> PAGE_SHIFT; index++) {
        page = find_get_page(mapping, index);
        if (!page)
            continue;
        memset(page_address(page), 0xFF, PAGE_SIZE);
        page_cache_release(page);
    }
    return 0;
}

static int logfs_mtd_erase(struct super_block *sb, loff_t ofs, size_t len,
        int ensure_write)
{
    struct mtd_info *mtd = logfs_super(sb)->s_mtd;
    struct erase_info ei;
    DECLARE_COMPLETION_ONSTACK(complete);
    int ret;

    BUG_ON(len % mtd->erasesize);
    if (logfs_super(sb)->s_flags & LOGFS_SB_FLAG_RO)
        return -EROFS;

    memset(&ei, 0, sizeof(ei));
    ei.mtd = mtd;
    ei.addr = ofs;
    ei.len = len;
    ei.callback = logfs_erase_callback;
    ei.priv = (long)&complete;
    ret = mtd_erase(mtd, &ei);
    if (ret)
        return -EIO;

    wait_for_completion(&complete);
    if (ei.state != MTD_ERASE_DONE)
        return -EIO;
    return logfs_mtd_erase_mapping(sb, ofs, len);
}

static void logfs_mtd_sync(struct super_block *sb)
{
    struct mtd_info *mtd = logfs_super(sb)->s_mtd;

    mtd_sync(mtd);
}

static int logfs_mtd_readpage(void *_sb, struct page *page)
{
    struct super_block *sb = _sb;
    int err;

    err = logfs_mtd_read(sb, page->index << PAGE_SHIFT, PAGE_SIZE,
            page_address(page));
    if (err == -EUCLEAN || err == -EBADMSG) {
        /* -EBADMSG happens regularly on power failures */
        err = 0;
        /* FIXME: force GC this segment */
    }
    if (err) {
        ClearPageUptodate(page);
        SetPageError(page);
    } else {
        SetPageUptodate(page);
        ClearPageError(page);
    }
    unlock_page(page);
    return err;
}

static struct page *logfs_mtd_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 = logfs_mtd_readpage;
    struct mtd_info *mtd = super->s_mtd;

    *ofs = 0;
    while (mtd_block_isbad(mtd, *ofs)) {
        *ofs += mtd->erasesize;
        if (*ofs >= mtd->size)
            return NULL;
    }
    BUG_ON(*ofs & ~PAGE_MASK);
    return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
}

static struct page *logfs_mtd_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 = logfs_mtd_readpage;
    struct mtd_info *mtd = super->s_mtd;

    *ofs = mtd->size - mtd->erasesize;
    while (mtd_block_isbad(mtd, *ofs)) {
        *ofs -= mtd->erasesize;
        if (*ofs <= 0)
            return NULL;
    }
    *ofs = *ofs + mtd->erasesize - 0x1000;
    BUG_ON(*ofs & ~PAGE_MASK);
    return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
}

static int __logfs_mtd_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 page *page;
    int i, err;

    for (i = 0; i < nr_pages; i++) {
        page = find_lock_page(mapping, index + i);
        BUG_ON(!page);

        err = loffs_mtd_write(sb, page->index << PAGE_SHIFT, PAGE_SIZE,
                    page_address(page));
        unlock_page(page);
        page_cache_release(page);
        if (err)
            return err;
    }
    return 0;
}

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

    if (super->s_flags & LOGFS_SB_FLAG_RO)
        return;

    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);
    __logfs_mtd_writeseg(sb, ofs, ofs >> PAGE_SHIFT, len >> PAGE_SHIFT);
}

static void logfs_mtd_put_device(struct logfs_super *s)
{
    put_mtd_device(s->s_mtd);
}

static int logfs_mtd_can_write_buf(struct super_block *sb, u64 ofs)
{
    struct logfs_super *super = logfs_super(sb);
    void *buf;
    int err;

    buf = kmalloc(super->s_writesize, GFP_KERNEL);
    if (!buf)
        return -ENOMEM;
    err = logfs_mtd_read(sb, ofs, super->s_writesize, buf);
    if (err)
        goto out;
    if (memchr_inv(buf, 0xff, super->s_writesize))
        err = -EIO;
    kfree(buf);
out:
    return err;
}

static const struct logfs_device_ops mtd_devops = {
    .find_first_sb  = logfs_mtd_find_first_sb,
    .find_last_sb   = logfs_mtd_find_last_sb,
    .readpage   = logfs_mtd_readpage,
    .writeseg   = logfs_mtd_writeseg,
    .erase      = logfs_mtd_erase,
    .can_write_buf  = logfs_mtd_can_write_buf,
    .sync       = logfs_mtd_sync,
    .put_device = logfs_mtd_put_device,
};

int logfs_get_sb_mtd(struct logfs_super *s, int mtdnr)
{
    struct mtd_info *mtd = get_mtd_device(NULL, mtdnr);
    if (IS_ERR(mtd))
        return PTR_ERR(mtd);

    s->s_bdev = NULL;
    s->s_mtd = mtd;
    s->s_devops = &mtd_devops;
    return 0;
}