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Message-ID: <20161229025835.GC21325@fieldses.org>
Date: Wed, 28 Dec 2016 21:58:35 -0500
From: bfields@...ldses.org (J. Bruce Fields)
To: Richard Weinberger <richard@....at>
Cc: linux-mtd@...ts.infradead.org, david@...ma-star.at, tytso@....edu,
dedekind1@...il.com, adrian.hunter@...el.com,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
adilger.kernel@...ger.ca, akpm@...ux-foundation.org,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/6] ubifs: Use 64bit readdir cookies
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@....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
>
> --
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