xattr.c

来自「Linux Kernel 2.6.9 for OMAP1710」· C语言 代码 · 共 1,455 行 · 第 1/3 页

/*
 * linux/fs/reiserfs/xattr.c
 *
 * Copyright (c) 2002 by Jeff Mahoney, <[e-mail]>
 *
 */

/*
 * In order to implement EA/ACLs in a clean, backwards compatible manner,
 * they are implemented as files in a "private" directory.
 * Each EA is in it's own file, with the directory layout like so (/ is assumed
 * to be relative to fs root). Inside the /.reiserfs_priv/xattrs directory,
 * directories named using the capital-hex form of the objectid and
 * generation number are used. Inside each directory are individual files
 * named with the name of the extended attribute.
 *
 * So, for objectid 12648430, we could have:
 * /.reiserfs_priv/xattrs/C0FFEE.0/system.posix_acl_access
 * /.reiserfs_priv/xattrs/C0FFEE.0/system.posix_acl_default
 * /.reiserfs_priv/xattrs/C0FFEE.0/user.Content-Type
 * .. or similar.
 *
 * The file contents are the text of the EA. The size is known based on the
 * stat data describing the file.
 *
 * In the case of system.posix_acl_access and system.posix_acl_default, since
 * these are special cases for filesystem ACLs, they are interpreted by the
 * kernel, in addition, they are negatively and positively cached and attached
 * to the inode so that unnecessary lookups are avoided.
 */

#include <linux/reiserfs_fs.h>
#include <linux/dcache.h>
#include <linux/namei.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/xattr.h>
#include <linux/reiserfs_xattr.h>
#include <linux/reiserfs_acl.h>
#include <linux/mbcache.h>
#include <asm/uaccess.h>
#include <asm/checksum.h>
#include <linux/smp_lock.h>
#include <linux/stat.h>
#include <asm/semaphore.h>

#define FL_READONLY 128
#define FL_DIR_SEM_HELD 256
#define PRIVROOT_NAME ".reiserfs_priv"
#define XAROOT_NAME   "xattrs"

static struct reiserfs_xattr_handler *find_xattr_handler_prefix (const char *prefix);

static struct dentry *
create_xa_root (struct super_block *sb)
{
    struct dentry *privroot = dget (REISERFS_SB(sb)->priv_root);
    struct dentry *xaroot;

    /* This needs to be created at mount-time */
    if (!privroot)
        return ERR_PTR(-EOPNOTSUPP);

    xaroot = lookup_one_len (XAROOT_NAME, privroot, strlen (XAROOT_NAME));
    if (IS_ERR (xaroot)) {
        goto out;
    } else if (!xaroot->d_inode) {
        int err;
        down (&privroot->d_inode->i_sem);
        err = privroot->d_inode->i_op->mkdir (privroot->d_inode, xaroot, 0700);
        up (&privroot->d_inode->i_sem);

        if (err) {
            dput (xaroot);
            dput (privroot);
            return ERR_PTR (err);
        }
        REISERFS_SB(sb)->xattr_root = dget (xaroot);
    }

out:
    dput (privroot);
    return xaroot;
}

/* This will return a dentry, or error, refering to the xa root directory.
 * If the xa root doesn't exist yet, the dentry will be returned without
 * an associated inode. This dentry can be used with ->mkdir to create
 * the xa directory. */
static struct dentry *
__get_xa_root (struct super_block *s)
{
    struct dentry *privroot = dget (REISERFS_SB(s)->priv_root);
    struct dentry *xaroot = NULL;

    if (IS_ERR (privroot) || !privroot)
        return privroot;

    xaroot = lookup_one_len (XAROOT_NAME, privroot, strlen (XAROOT_NAME));
    if (IS_ERR (xaroot)) {
        goto out;
    } else if (!xaroot->d_inode) {
        dput (xaroot);
        xaroot = NULL;
        goto out;
    }

    REISERFS_SB(s)->xattr_root = dget (xaroot);

out:
    dput (privroot);
    return xaroot;
}

/* Returns the dentry (or NULL) referring to the root of the extended
 * attribute directory tree. If it has already been retreived, it is used.
 * Otherwise, we attempt to retreive it from disk. It may also return
 * a pointer-encoded error.
 */
static inline struct dentry *
get_xa_root (struct super_block *s)
{
    struct dentry *dentry = dget (REISERFS_SB(s)->xattr_root);

    if (!dentry)
        dentry = __get_xa_root (s);

    return dentry;
}

/* Opens the directory corresponding to the inode's extended attribute store.
 * If flags allow, the tree to the directory may be created. If creation is
 * prohibited, -ENODATA is returned. */
static struct dentry *
open_xa_dir (const struct inode *inode, int flags)
{
    struct dentry *xaroot, *xadir;
    char namebuf[17];

    xaroot = get_xa_root (inode->i_sb);
    if (IS_ERR (xaroot)) {
        return xaroot;
    } else if (!xaroot) {
        if (flags == 0 || flags & XATTR_CREATE) {
            xaroot = create_xa_root (inode->i_sb);
            if (IS_ERR (xaroot))
                return xaroot;
        }
        if (!xaroot)
            return ERR_PTR (-ENODATA);
    }

    /* ok, we have xaroot open */

    snprintf (namebuf, sizeof (namebuf), "%X.%X",
              le32_to_cpu (INODE_PKEY (inode)->k_objectid),
              inode->i_generation);
    xadir = lookup_one_len (namebuf, xaroot, strlen (namebuf));
    if (IS_ERR (xadir)) {
        dput (xaroot);
        return xadir;
    }

    if (!xadir->d_inode) {
        int err;
        if (flags == 0 || flags & XATTR_CREATE) {
            /* Although there is nothing else trying to create this directory,
             * another directory with the same hash may be created, so we need
             * to protect against that */
            err = xaroot->d_inode->i_op->mkdir (xaroot->d_inode, xadir, 0700);
            if (err) {
                dput (xaroot);
                dput (xadir);
                return ERR_PTR (err);
            }
        }
        if (!xadir->d_inode) {
            dput (xaroot);
            dput (xadir);
            return ERR_PTR (-ENODATA);
        }
        /* Newly created object.. Need to mark it private */
        REISERFS_I(xadir->d_inode)->i_flags |= i_priv_object;
    }

    dput (xaroot);
    return xadir;
}

/* Returns a dentry corresponding to a specific extended attribute file
 * for the inode. If flags allow, the file is created. Otherwise, a
 * valid or negative dentry, or an error is returned. */
static struct dentry *
get_xa_file_dentry (const struct inode *inode, const char *name, int flags)
{
    struct dentry *xadir, *xafile;
    int err = 0;

    xadir = open_xa_dir (inode, flags);
    if (IS_ERR (xadir)) {
        return ERR_PTR (PTR_ERR (xadir));
    } else if (xadir && !xadir->d_inode) {
        dput (xadir);
        return ERR_PTR (-ENODATA);
    }

    xafile = lookup_one_len (name, xadir, strlen (name));
    if (IS_ERR (xafile)) {
        dput (xadir);
        return ERR_PTR (PTR_ERR (xafile));
    }

    if (xafile->d_inode) { /* file exists */
        if (flags & XATTR_CREATE) {
            err = -EEXIST;
            dput (xafile);
            goto out;
        }
    } else if (flags & XATTR_REPLACE || flags & FL_READONLY) {
        goto out;
    } else {
        /* inode->i_sem is down, so nothing else can try to create
         * the same xattr */
        err = xadir->d_inode->i_op->create (xadir->d_inode, xafile,
                                            0700|S_IFREG, NULL);

        if (err) {
            dput (xafile);
            goto out;
        }
        /* Newly created object.. Need to mark it private */
        REISERFS_I(xafile->d_inode)->i_flags |= i_priv_object;
    }

out:
    dput (xadir);
    if (err)
        xafile = ERR_PTR (err);
    return xafile;
}


/* Opens a file pointer to the attribute associated with inode */
static struct file *
open_xa_file (const struct inode *inode, const char *name, int flags)
{
    struct dentry *xafile;
    struct file *fp;

    xafile = get_xa_file_dentry (inode, name, flags);
    if (IS_ERR (xafile))
        return ERR_PTR (PTR_ERR (xafile));
    else if (!xafile->d_inode) {
        dput (xafile);
        return ERR_PTR (-ENODATA);
    }

    fp = dentry_open (xafile, NULL, O_RDWR);
    /* dentry_open dputs the dentry if it fails */

    return fp;
}


/*
 * this is very similar to fs/reiserfs/dir.c:reiserfs_readdir, but
 * we need to drop the path before calling the filldir struct.  That
 * would be a big performance hit to the non-xattr case, so I've copied
 * the whole thing for now. --clm
 *
 * the big difference is that I go backwards through the directory,
 * and don't mess with f->f_pos, but the idea is the same.  Do some
 * action on each and every entry in the directory.
 *
 * we're called with i_sem held, so there are no worries about the directory
 * changing underneath us.
 */
static int __xattr_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
    struct inode *inode = filp->f_dentry->d_inode;
    struct cpu_key pos_key;	/* key of current position in the directory (key of directory entry) */
    INITIALIZE_PATH (path_to_entry);
    struct buffer_head * bh;
    int entry_num;
    struct item_head * ih, tmp_ih;
    int search_res;
    char * local_buf;
    loff_t next_pos;
    char small_buf[32] ; /* avoid kmalloc if we can */
    struct reiserfs_de_head *deh;
    int d_reclen;
    char * d_name;
    off_t d_off;
    ino_t d_ino;
    struct reiserfs_dir_entry de;


    /* form key for search the next directory entry using f_pos field of
       file structure */
    next_pos = max_reiserfs_offset(inode);

    while (1) {
research:
	if (next_pos <= DOT_DOT_OFFSET)
	    break;
	make_cpu_key (&pos_key, inode, next_pos, TYPE_DIRENTRY, 3);

	search_res = search_by_entry_key(inode->i_sb, &pos_key, &path_to_entry, &de);
	if (search_res == IO_ERROR) {
	    // FIXME: we could just skip part of directory which could
	    // not be read
	    pathrelse(&path_to_entry);
	    return -EIO;
	}

	if (search_res == NAME_NOT_FOUND)
	    de.de_entry_num--;

	set_de_name_and_namelen(&de);
	entry_num = de.de_entry_num;
	deh = &(de.de_deh[entry_num]);

	bh = de.de_bh;
	ih = de.de_ih;

	if (!is_direntry_le_ih(ih)) {
            reiserfs_warning(inode->i_sb, "not direntry %h", ih);
	    break;
        }
	copy_item_head(&tmp_ih, ih);

	/* we must have found item, that is item of this directory, */
	RFALSE( COMP_SHORT_KEYS (&(ih->ih_key), &pos_key),
		"vs-9000: found item %h does not match to dir we readdir %K",
		ih, &pos_key);

	if (deh_offset(deh) <= DOT_DOT_OFFSET) {
	    break;
	}

	/* look for the previous entry in the directory */
	next_pos = deh_offset (deh) - 1;

	if (!de_visible (deh))
	    /* it is hidden entry */
	    continue;

	d_reclen = entry_length(bh, ih, entry_num);
	d_name = B_I_DEH_ENTRY_FILE_NAME (bh, ih, deh);
	d_off = deh_offset (deh);
	d_ino = deh_objectid (deh);

	if (!d_name[d_reclen - 1])
	    d_reclen = strlen (d_name);

	if (d_reclen > REISERFS_MAX_NAME(inode->i_sb->s_blocksize)){
	    /* too big to send back to VFS */
	    continue ;
	}

        /* Ignore the .reiserfs_priv entry */
        if (reiserfs_xattrs (inode->i_sb) &&
            !old_format_only(inode->i_sb) &&
            deh_objectid (deh) == le32_to_cpu (INODE_PKEY(REISERFS_SB(inode->i_sb)->priv_root->d_inode)->k_objectid))
          continue;

	if (d_reclen <= 32) {
	  local_buf = small_buf ;
	} else {
	    local_buf = reiserfs_kmalloc(d_reclen, GFP_NOFS, inode->i_sb) ;
	    if (!local_buf) {
		pathrelse (&path_to_entry);
		return -ENOMEM ;
	    }
	    if (item_moved (&tmp_ih, &path_to_entry)) {
		reiserfs_kfree(local_buf, d_reclen, inode->i_sb) ;

		/* sigh, must retry.  Do this same offset again */
		next_pos = d_off;
		goto research;
	    }
	}

	// Note, that we copy name to user space via temporary
	// buffer (local_buf) because filldir will block if
	// user space buffer is swapped out. At that time
	// entry can move to somewhere else
	memcpy (local_buf, d_name, d_reclen);

	/* the filldir function might need to start transactions,
	 * or do who knows what.  Release the path now that we've
	 * copied all the important stuff out of the deh
	 */
	pathrelse (&path_to_entry);

	if (filldir (dirent, local_buf, d_reclen, d_off, d_ino,
		     DT_UNKNOWN) < 0) {
	    if (local_buf != small_buf) {
		reiserfs_kfree(local_buf, d_reclen, inode->i_sb) ;
	    }
	    goto end;
	}
	if (local_buf != small_buf) {
	    reiserfs_kfree(local_buf, d_reclen, inode->i_sb) ;
	}
    } /* while */

end:
    pathrelse (&path_to_entry);
    return 0;
}

/*
 * this could be done with dedicated readdir ops for the xattr files,
 * but I want to get something working asap
 * this is stolen from vfs_readdir
 *
 */
static
int xattr_readdir(struct file *file, filldir_t filler, void *buf)
{
        struct inode *inode = file->f_dentry->d_inode;
        int res = -ENOTDIR;
        if (!file->f_op || !file->f_op->readdir)
                goto out;
        down(&inode->i_sem);
//        down(&inode->i_zombie);
        res = -ENOENT;
        if (!IS_DEADDIR(inode)) {
                lock_kernel();
                res = __xattr_readdir(file, buf, filler);
                unlock_kernel();
        }
//        up(&inode->i_zombie);
        up(&inode->i_sem);
out:
        return res;
}


/* Internal operations on file data */
static inline void
reiserfs_put_page(struct page *page)
{
        kunmap(page);
        page_cache_release(page);
}

static struct page *
reiserfs_get_page(struct inode *dir, unsigned long n)
{
        struct address_space *mapping = dir->i_mapping;
        struct page *page;
        /* We can deadlock if we try to free dentries,
           and an unlink/rmdir has just occured - GFP_NOFS avoids this */
        mapping->flags = (mapping->flags & ~__GFP_BITS_MASK) | GFP_NOFS;
        page = read_cache_page (mapping, n,
                                (filler_t*)mapping->a_ops->readpage, NULL);
        if (!IS_ERR(page)) {
                wait_on_page_locked(page);
                kmap(page);
                if (!PageUptodate(page))
                        goto fail;

                if (PageError(page))
                        goto fail;
        }
        return page;

fail:
        reiserfs_put_page(page);
        return ERR_PTR(-EIO);
}

static inline __u32
xattr_hash (const char *msg, int len)
{
    return csum_partial (msg, len, 0);
}

/* Generic extended attribute operations that can be used by xa plugins */

/*