dir.c

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/*
 *  linux/fs/sysv/dir.c
 *
 *  minix/dir.c
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  coh/dir.c
 *  Copyright (C) 1993  Pascal Haible, Bruno Haible
 *
 *  sysv/dir.c
 *  Copyright (C) 1993  Bruno Haible
 *
 *  SystemV/Coherent directory handling functions
 */

#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/swap.h>
#include "sysv.h"

static int sysv_readdir(struct file *, void *, filldir_t);

const struct file_operations sysv_dir_operations = {
    .llseek     = generic_file_llseek,
    .read       = generic_read_dir,
    .readdir    = sysv_readdir,
    .fsync      = generic_file_fsync,
};

static inline void dir_put_page(struct page *page)
{
    kunmap(page);
    page_cache_release(page);
}

static inline unsigned long dir_pages(struct inode *inode)
{
    return (inode->i_size+PAGE_CACHE_SIZE-1)>>PAGE_CACHE_SHIFT;
}

static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
{
    struct address_space *mapping = page->mapping;
    struct inode *dir = mapping->host;
    int err = 0;

    block_write_end(NULL, mapping, pos, len, len, page, NULL);
    if (pos+len > dir->i_size) {
        i_size_write(dir, pos+len);
        mark_inode_dirty(dir);
    }
    if (IS_DIRSYNC(dir))
        err = write_one_page(page, 1);
    else
        unlock_page(page);
    return err;
}

static struct page * dir_get_page(struct inode *dir, unsigned long n)
{
    struct address_space *mapping = dir->i_mapping;
    struct page *page = read_mapping_page(mapping, n, NULL);
    if (!IS_ERR(page))
        kmap(page);
    return page;
}

static int sysv_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
    unsigned long pos = filp->f_pos;
    struct inode *inode = filp->f_path.dentry->d_inode;
    struct super_block *sb = inode->i_sb;
    unsigned offset = pos & ~PAGE_CACHE_MASK;
    unsigned long n = pos >> PAGE_CACHE_SHIFT;
    unsigned long npages = dir_pages(inode);

    pos = (pos + SYSV_DIRSIZE-1) & ~(SYSV_DIRSIZE-1);
    if (pos >= inode->i_size)
        goto done;

    for ( ; n < npages; n++, offset = 0) {
        char *kaddr, *limit;
        struct sysv_dir_entry *de;
        struct page *page = dir_get_page(inode, n);

        if (IS_ERR(page))
            continue;
        kaddr = (char *)page_address(page);
        de = (struct sysv_dir_entry *)(kaddr+offset);
        limit = kaddr + PAGE_CACHE_SIZE - SYSV_DIRSIZE;
        for ( ;(char*)de <= limit; de++) {
            char *name = de->name;
            int over;

            if (!de->inode)
                continue;

            offset = (char *)de - kaddr;

            over = filldir(dirent, name, strnlen(name,SYSV_NAMELEN),
                    ((loff_t)n<<PAGE_CACHE_SHIFT) | offset,
                    fs16_to_cpu(SYSV_SB(sb), de->inode),
                    DT_UNKNOWN);
            if (over) {
                dir_put_page(page);
                goto done;
            }
        }
        dir_put_page(page);
    }

done:
    filp->f_pos = ((loff_t)n << PAGE_CACHE_SHIFT) | offset;
    return 0;
}

/* compare strings: name[0..len-1] (not zero-terminated) and
 * buffer[0..] (filled with zeroes up to buffer[0..maxlen-1])
 */
static inline int namecompare(int len, int maxlen,
    const char * name, const char * buffer)
{
    if (len < maxlen && buffer[len])
        return 0;
    return !memcmp(name, buffer, len);
}

/*
 *  sysv_find_entry()
 *
 * finds an entry in the specified directory with the wanted name. It
 * returns the cache buffer in which the entry was found, and the entry
 * itself (as a parameter - res_dir). It does NOT read the inode of the
 * entry - you'll have to do that yourself if you want to.
 */
struct sysv_dir_entry *sysv_find_entry(struct dentry *dentry, struct page **res_page)
{
    const char * name = dentry->d_name.name;
    int namelen = dentry->d_name.len;
    struct inode * dir = dentry->d_parent->d_inode;
    unsigned long start, n;
    unsigned long npages = dir_pages(dir);
    struct page *page = NULL;
    struct sysv_dir_entry *de;

    *res_page = NULL;

    start = SYSV_I(dir)->i_dir_start_lookup;
    if (start >= npages)
        start = 0;
    n = start;

    do {
        char *kaddr;
        page = dir_get_page(dir, n);
        if (!IS_ERR(page)) {
            kaddr = (char*)page_address(page);
            de = (struct sysv_dir_entry *) kaddr;
            kaddr += PAGE_CACHE_SIZE - SYSV_DIRSIZE;
            for ( ; (char *) de <= kaddr ; de++) {
                if (!de->inode)
                    continue;
                if (namecompare(namelen, SYSV_NAMELEN,
                            name, de->name))
                    goto found;
            }
            dir_put_page(page);
        }

        if (++n >= npages)
            n = 0;
    } while (n != start);

    return NULL;

found:
    SYSV_I(dir)->i_dir_start_lookup = n;
    *res_page = page;
    return de;
}

int sysv_add_link(struct dentry *dentry, struct inode *inode)
{
    struct inode *dir = dentry->d_parent->d_inode;
    const char * name = dentry->d_name.name;
    int namelen = dentry->d_name.len;
    struct page *page = NULL;
    struct sysv_dir_entry * de;
    unsigned long npages = dir_pages(dir);
    unsigned long n;
    char *kaddr;
    loff_t pos;
    int err;

    /* We take care of directory expansion in the same loop */
    for (n = 0; n <= npages; n++) {
        page = dir_get_page(dir, n);
        err = PTR_ERR(page);
        if (IS_ERR(page))
            goto out;
        kaddr = (char*)page_address(page);
        de = (struct sysv_dir_entry *)kaddr;
        kaddr += PAGE_CACHE_SIZE - SYSV_DIRSIZE;
        while ((char *)de <= kaddr) {
            if (!de->inode)
                goto got_it;
            err = -EEXIST;
            if (namecompare(namelen, SYSV_NAMELEN, name, de->name)) 
                goto out_page;
            de++;
        }
        dir_put_page(page);
    }
    BUG();
    return -EINVAL;

got_it:
    pos = page_offset(page) +
            (char*)de - (char*)page_address(page);
    lock_page(page);
    err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
    if (err)
        goto out_unlock;
    memcpy (de->name, name, namelen);
    memset (de->name + namelen, 0, SYSV_DIRSIZE - namelen - 2);
    de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), inode->i_ino);
    err = dir_commit_chunk(page, pos, SYSV_DIRSIZE);
    dir->i_mtime = dir->i_ctime = CURRENT_TIME_SEC;
    mark_inode_dirty(dir);
out_page:
    dir_put_page(page);
out:
    return err;
out_unlock:
    unlock_page(page);
    goto out_page;
}

int sysv_delete_entry(struct sysv_dir_entry *de, struct page *page)
{
    struct inode *inode = page->mapping->host;
    char *kaddr = (char*)page_address(page);
    loff_t pos = page_offset(page) + (char *)de - kaddr;
    int err;

    lock_page(page);
    err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
    BUG_ON(err);
    de->inode = 0;
    err = dir_commit_chunk(page, pos, SYSV_DIRSIZE);
    dir_put_page(page);
    inode->i_ctime = inode->i_mtime = CURRENT_TIME_SEC;
    mark_inode_dirty(inode);
    return err;
}

int sysv_make_empty(struct inode *inode, struct inode *dir)
{
    struct page *page = grab_cache_page(inode->i_mapping, 0);
    struct sysv_dir_entry * de;
    char *base;
    int err;

    if (!page)
        return -ENOMEM;
    err = sysv_prepare_chunk(page, 0, 2 * SYSV_DIRSIZE);
    if (err) {
        unlock_page(page);
        goto fail;
    }
    kmap(page);

    base = (char*)page_address(page);
    memset(base, 0, PAGE_CACHE_SIZE);

    de = (struct sysv_dir_entry *) base;
    de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), inode->i_ino);
    strcpy(de->name,".");
    de++;
    de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), dir->i_ino);
    strcpy(de->name,"..");

    kunmap(page);
    err = dir_commit_chunk(page, 0, 2 * SYSV_DIRSIZE);
fail:
    page_cache_release(page);
    return err;
}

/*
 * routine to check that the specified directory is empty (for rmdir)
 */
int sysv_empty_dir(struct inode * inode)
{
    struct super_block *sb = inode->i_sb;
    struct page *page = NULL;
    unsigned long i, npages = dir_pages(inode);

    for (i = 0; i < npages; i++) {
        char *kaddr;
        struct sysv_dir_entry * de;
        page = dir_get_page(inode, i);

        if (IS_ERR(page))
            continue;

        kaddr = (char *)page_address(page);
        de = (struct sysv_dir_entry *)kaddr;
        kaddr += PAGE_CACHE_SIZE-SYSV_DIRSIZE;

        for ( ;(char *)de <= kaddr; de++) {
            if (!de->inode)
                continue;
            /* check for . and .. */
            if (de->name[0] != '.')
                goto not_empty;
            if (!de->name[1]) {
                if (de->inode == cpu_to_fs16(SYSV_SB(sb),
                            inode->i_ino))
                    continue;
                goto not_empty;
            }
            if (de->name[1] != '.' || de->name[2])
                goto not_empty;
        }
        dir_put_page(page);
    }
    return 1;

not_empty:
    dir_put_page(page);
    return 0;
}

/* Releases the page */
void sysv_set_link(struct sysv_dir_entry *de, struct page *page,
    struct inode *inode)
{
    struct inode *dir = page->mapping->host;
    loff_t pos = page_offset(page) +
            (char *)de-(char*)page_address(page);
    int err;

    lock_page(page);
    err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
    BUG_ON(err);
    de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), inode->i_ino);
    err = dir_commit_chunk(page, pos, SYSV_DIRSIZE);
    dir_put_page(page);
    dir->i_mtime = dir->i_ctime = CURRENT_TIME_SEC;
    mark_inode_dirty(dir);
}

struct sysv_dir_entry * sysv_dotdot (struct inode *dir, struct page **p)
{
    struct page *page = dir_get_page(dir, 0);
    struct sysv_dir_entry *de = NULL;

    if (!IS_ERR(page)) {
        de = (struct sysv_dir_entry*) page_address(page) + 1;
        *p = page;
    }
    return de;
}

ino_t sysv_inode_by_name(struct dentry *dentry)
{
    struct page *page;
    struct sysv_dir_entry *de = sysv_find_entry (dentry, &page);
    ino_t res = 0;
    
    if (de) {
        res = fs16_to_cpu(SYSV_SB(dentry->d_sb), de->inode);
        dir_put_page(page);
    }
    return res;
}