Re: [PATCH 3/6] ubifs: Use 64bit readdir cookies

[bfields@fieldses.org (J. Bruce Fields)]

On Thu, Dec 01, 2016 at 11:02:18PM +0100, Richard Weinberger wrote:
> This is the first step to support proper telldir/seekdir()
> in UBIFS.
> Let's report 64bit cookies in readdir(). The cookie is a combination
> of the entry key plus the double hash value.

Would it be possible to explain what that means in a little detail, for
a ubifs-ignoramus?

I'm just curious how it meets the requirements for nfs exports.

--b.

> 
> Signed-off-by: Richard Weinberger <richard@nod.at>
> ---
>  fs/ubifs/dir.c   | 46 +++++++++++++++++++++++++++++++------------
>  fs/ubifs/key.h   | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/ubifs/ubifs.h |  1 +
>  3 files changed, 94 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
> index 883b2fdf51df..3b8c08dad75b 100644
> --- a/fs/ubifs/dir.c
> +++ b/fs/ubifs/dir.c
> @@ -539,7 +539,7 @@ static int ubifs_readdir(struct file *file, struct dir_context *ctx)
>  
>  	dbg_gen("dir ino %lu, f_pos %#llx", dir->i_ino, ctx->pos);
>  
> -	if (ctx->pos > UBIFS_S_KEY_HASH_MASK || ctx->pos == 2)
> +	if (ctx->pos == 2)
>  		/*
>  		 * The directory was seek'ed to a senseless position or there
>  		 * are no more entries.
> @@ -594,7 +594,7 @@ static int ubifs_readdir(struct file *file, struct dir_context *ctx)
>  			goto out;
>  		}
>  
> -		ctx->pos = key_hash_flash(c, &dent->key);
> +		ctx->pos = key_get_dir_pos(c, file, dent);
>  		file->private_data = dent;
>  	}
>  
> @@ -604,21 +604,43 @@ static int ubifs_readdir(struct file *file, struct dir_context *ctx)
>  		 * The directory was seek'ed to and is now readdir'ed.
>  		 * Find the entry corresponding to @ctx->pos or the closest one.
>  		 */
> -		dent_key_init_hash(c, &key, dir->i_ino, ctx->pos);
> -		fname_len(&nm) = 0;
> -		dent = ubifs_tnc_next_ent(c, &key, &nm);
> -		if (IS_ERR(dent)) {
> -			err = PTR_ERR(dent);
> -			goto out;
> +		dent_key_init_hash(c, &key, dir->i_ino,
> +				   key_get_hash_from_dir_pos(c, file, ctx->pos));
> +
> +		if (key_want_short_hash(file)) {
> +			err = -ENOENT;
> +		} else {
> +			dent = kmalloc(UBIFS_MAX_DENT_NODE_SZ, GFP_NOFS);
> +			if (!dent) {
> +				err = -ENOMEM;
> +				goto out;
> +			}
> +
> +			err = ubifs_tnc_lookup_dh(c, &key, dent,
> +				key_get_cookie_from_dir_pos(c, ctx->pos));
> +		}
> +		if (err) {
> +			kfree(dent);
> +
> +			if (err < 0 && err != -ENOENT && err != -EOPNOTSUPP)
> +				goto out;
> +
> +			fname_len(&nm) = 0;
> +			dent = ubifs_tnc_next_ent(c, &key, &nm);
> +			if (IS_ERR(dent)) {
> +				err = PTR_ERR(dent);
> +				goto out;
> +			}
>  		}
> -		ctx->pos = key_hash_flash(c, &dent->key);
> +
> +		ctx->pos = key_get_dir_pos(c, file, dent);
>  		file->private_data = dent;
>  	}
>  
>  	while (1) {
> -		dbg_gen("feed '%s', ino %llu, new f_pos %#x",
> +		dbg_gen("feed '%s', ino %llu, new f_pos %#lx",
>  			dent->name, (unsigned long long)le64_to_cpu(dent->inum),
> -			key_hash_flash(c, &dent->key));
> +			(unsigned long)key_get_dir_pos(c, file, dent));
>  		ubifs_assert(le64_to_cpu(dent->ch.sqnum) >
>  			     ubifs_inode(dir)->creat_sqnum);
>  
> @@ -656,7 +678,7 @@ static int ubifs_readdir(struct file *file, struct dir_context *ctx)
>  		}
>  
>  		kfree(file->private_data);
> -		ctx->pos = key_hash_flash(c, &dent->key);
> +		ctx->pos = key_get_dir_pos(c, file, dent);
>  		file->private_data = dent;
>  		cond_resched();
>  	}
> diff --git a/fs/ubifs/key.h b/fs/ubifs/key.h
> index 7547be512db2..2788e36ce832 100644
> --- a/fs/ubifs/key.h
> +++ b/fs/ubifs/key.h
> @@ -397,6 +397,65 @@ static inline uint32_t key_hash_flash(const struct ubifs_info *c, const void *k)
>  }
>  
>  /**
> + * key_want_short_hash - tests whether we can emit a 64bit hash or not.
> + * @file: the file handle of the directory
> + */
> +static inline bool key_want_short_hash(struct file *file)
> +{
> +	if (file->f_mode & FMODE_32BITHASH)
> +		return true;
> +
> +	if (!(file->f_mode & FMODE_64BITHASH) && is_32bit_api())
> +		return true;
> +
> +	return false;
> +}
> +
> +/**
> + * key_dir_pos - compute a 64bit directory cookie for readdir()
> + * @c: UBIFS file-system description object
> + * @file: the file handle of the directory
> + * @dent: the directory entry
> + */
> +static inline loff_t key_get_dir_pos(const struct ubifs_info *c,
> +				     struct file *file,
> +				     struct ubifs_dent_node *dent)
> +{
> +	BUILD_BUG_ON(sizeof(loff_t) < 8);
> +
> +	if (key_want_short_hash(file))
> +		return key_hash_flash(c, &dent->key);
> +
> +	return ((loff_t)key_hash_flash(c, &dent->key)) << UBIFS_DH_BITS | le32_to_cpu(dent->cookie);
> +}
> +
> +/**
> + * key_get_hash_from_dir_pos - extracts the flash key from a directory offset.
> + * @c: UBIFS file-system description object
> + * @file: the file handle of the directory
> + * @pos: the directory offset provied by VFS
> + */
> +static inline uint32_t key_get_hash_from_dir_pos(const struct ubifs_info *c,
> +						 struct file *file, loff_t pos)
> +{
> +	if (key_want_short_hash(file))
> +		return pos & UBIFS_S_KEY_HASH_MASK;
> +
> +	return (pos >> UBIFS_DH_BITS) & UBIFS_S_KEY_HASH_MASK;
> +}
> +
> +/**
> + * key_get_cookie_from_dir_pos - extracts the double hash cookie from a directory offset.
> + * @c: UBIFS file-system description object
> + * @pos: the directory offset provied by VFS
> + */
> +static inline uint32_t key_get_cookie_from_dir_pos(const struct ubifs_info *c,
> +						   loff_t pos)
> +{
> +	return pos & UBIFS_DH_MASK;
> +}
> +
> +/**
>   * key_block - get data block number.
>   * @c: UBIFS file-system description object
>   * @key: the key to get the block number from
> diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
> index 12f3df3ced0e..0532a6f82b1d 100644
> --- a/fs/ubifs/ubifs.h
> +++ b/fs/ubifs/ubifs.h
> @@ -40,6 +40,7 @@
>  #include <linux/xattr.h>
>  #include <linux/fscrypto.h>
>  #include <linux/random.h>
> +#include <linux/compat.h>
>  #include "ubifs-media.h"
>  
>  /* Version of this UBIFS implementation */
> -- 
> 2.7.3
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html