| Message ID | 20250319031545.2999807-2-neil@brown.name (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | tidy up various VFS lookup functions | expand |
On Wed, 19 Mar 2025 14:01:32 +1100, NeilBrown wrote: > The family of functions: > lookup_one() > lookup_one_unlocked() > lookup_one_positive_unlocked() > > appear designed to be used by external clients of the filesystem rather > than by filesystems acting on themselves as the lookup_one_len family > are used. > > [...] Applied to the vfs-6.16.async.dir branch of the vfs/vfs.git tree. Patches in the vfs-6.16.async.dir branch should appear in linux-next soon. Please report any outstanding bugs that were missed during review in a new review to the original patch series allowing us to drop it. It's encouraged to provide Acked-bys and Reviewed-bys even though the patch has now been applied. If possible patch trailers will be updated. Note that commit hashes shown below are subject to change due to rebase, trailer updates or similar. If in doubt, please check the listed branch. tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git branch: vfs-6.16.async.dir [1/6] VFS: improve interface for lookup_one functions https://git.kernel.org/vfs/vfs/c/d01d332dbf28 [2/6] nfsd: Use lookup_one() rather than lookup_one_len() https://git.kernel.org/vfs/vfs/c/4c664a5962b7 [3/6] cachefiles: Use lookup_one() rather than lookup_one_len() https://git.kernel.org/vfs/vfs/c/ebc0dcbf5ba2 [4/6] VFS: rename lookup_one_len family to lookup_noperm and remove permission check https://git.kernel.org/vfs/vfs/c/12597aa5fea6 [5/6] Use try_lookup_noperm() instead of d_hash_and_lookup() outside of VFS https://git.kernel.org/vfs/vfs/c/d2bacbb4495a [6/6] VFS: change lookup_one_common and lookup_noperm_common to take a qstr https://git.kernel.org/vfs/vfs/c/b496b0712e63
On Wed, 2025-03-19 at 14:01 +1100, NeilBrown wrote: > The family of functions: > lookup_one() > lookup_one_unlocked() > lookup_one_positive_unlocked() > > appear designed to be used by external clients of the filesystem rather > than by filesystems acting on themselves as the lookup_one_len family > are used. > > They are used by: > btrfs/ioctl - which is a user-space interface rather than an internal > activity > exportfs - i.e. from nfsd or the open_by_handle_at interface > overlayfs - at access the underlying filesystems > smb/server - for file service > > They should be used by nfsd (more than just the exportfs path) and > cachefs but aren't. > > It would help if the documentation didn't claim they should "not be > called by generic code". > I read that as generic VFS code, since this is really intended to used outside that, but I agree the term "generic" is vague here. > Also the path component name is passed as "name" and "len" which are > (confusingly?) separate by the "base". In some cases the len in simply > "strlen" and so passing a qstr using QSTR() would make the calling > clearer. > Other callers do pass separate name and len which are stored in a > struct. Sometimes these are already stored in a qstr, other times it > easily could be. > > So this patch changes these three functions to receive a 'struct qstr', > and improves the documentation. > > QSTR_LEN() is added to make it easy to pass a QSTR containing a known > len. > > Signed-off-by: NeilBrown <neil@brown.name> > --- > Documentation/filesystems/porting.rst | 9 +++++ > fs/btrfs/ioctl.c | 9 ++--- > fs/exportfs/expfs.c | 5 ++- > fs/namei.c | 51 ++++++++++++--------------- > fs/overlayfs/namei.c | 10 +++--- > fs/overlayfs/overlayfs.h | 2 +- > fs/overlayfs/readdir.c | 9 ++--- > fs/smb/server/smb2pdu.c | 7 ++-- > include/linux/dcache.h | 3 +- > include/linux/namei.h | 9 +++-- > 10 files changed, 57 insertions(+), 57 deletions(-) > > diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst > index 6817614e0820..06296ffd1e81 100644 > --- a/Documentation/filesystems/porting.rst > +++ b/Documentation/filesystems/porting.rst > @@ -1196,3 +1196,12 @@ should use d_drop();d_splice_alias() and return the result of the latter. > If a positive dentry cannot be returned for some reason, in-kernel > clients such as cachefiles, nfsd, smb/server may not perform ideally but > will fail-safe. > + > +--- > + > +** mandatory** > + > +lookup_one(), lookup_one_unlocked(), lookup_one_positive_unlocked() now > +take a qstr instead of a name and len. These, not the "one_len" > +versions, should be used whenever accessing a filesystem from outside > +that filesysmtem, through a mount point - which will have a mnt_idmap. > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c > index 6c18bad53cd3..f94b638f9478 100644 > --- a/fs/btrfs/ioctl.c > +++ b/fs/btrfs/ioctl.c > @@ -911,7 +911,7 @@ static noinline int btrfs_mksubvol(const struct path *parent, > if (error == -EINTR) > return error; > > - dentry = lookup_one(idmap, name, parent->dentry, namelen); > + dentry = lookup_one(idmap, QSTR_LEN(name, namelen), parent->dentry); > error = PTR_ERR(dentry); > if (IS_ERR(dentry)) > goto out_unlock; > @@ -2289,7 +2289,6 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, > struct btrfs_ioctl_vol_args_v2 *vol_args2 = NULL; > struct mnt_idmap *idmap = file_mnt_idmap(file); > char *subvol_name, *subvol_name_ptr = NULL; > - int subvol_namelen; > int ret = 0; > bool destroy_parent = false; > > @@ -2412,10 +2411,8 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, > goto out; > } > > - subvol_namelen = strlen(subvol_name); > - > if (strchr(subvol_name, '/') || > - strncmp(subvol_name, "..", subvol_namelen) == 0) { > + strcmp(subvol_name, "..") == 0) { > ret = -EINVAL; > goto free_subvol_name; > } > @@ -2428,7 +2425,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, > ret = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT); > if (ret == -EINTR) > goto free_subvol_name; > - dentry = lookup_one(idmap, subvol_name, parent, subvol_namelen); > + dentry = lookup_one(idmap, QSTR(subvol_name), parent); > if (IS_ERR(dentry)) { > ret = PTR_ERR(dentry); > goto out_unlock_dir; > diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c > index 0c899cfba578..974b432087aa 100644 > --- a/fs/exportfs/expfs.c > +++ b/fs/exportfs/expfs.c > @@ -145,7 +145,7 @@ static struct dentry *reconnect_one(struct vfsmount *mnt, > if (err) > goto out_err; > dprintk("%s: found name: %s\n", __func__, nbuf); > - tmp = lookup_one_unlocked(mnt_idmap(mnt), nbuf, parent, strlen(nbuf)); > + tmp = lookup_one_unlocked(mnt_idmap(mnt), QSTR(nbuf), parent); > if (IS_ERR(tmp)) { > dprintk("lookup failed: %ld\n", PTR_ERR(tmp)); > err = PTR_ERR(tmp); > @@ -551,8 +551,7 @@ exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, > } > > inode_lock(target_dir->d_inode); > - nresult = lookup_one(mnt_idmap(mnt), nbuf, > - target_dir, strlen(nbuf)); > + nresult = lookup_one(mnt_idmap(mnt), QSTR(nbuf), target_dir); > if (!IS_ERR(nresult)) { > if (unlikely(nresult->d_inode != result->d_inode)) { > dput(nresult); > diff --git a/fs/namei.c b/fs/namei.c > index b5abf456c5f4..75816fa80028 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -2922,19 +2922,17 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) > EXPORT_SYMBOL(lookup_one_len); > > /** > - * lookup_one - filesystem helper to lookup single pathname component > + * lookup_one - lookup single pathname component > * @idmap: idmap of the mount the lookup is performed from > - * @name: pathname component to lookup > + * @name: qstr holding pathname component to lookup > * @base: base directory to lookup from > - * @len: maximum length @len should be interpreted to > * > - * Note that this routine is purely a helper for filesystem usage and should > - * not be called by generic code. > + * This can be used for in-kernel filesystem clients such as file servers. > * > * The caller must hold base->i_mutex. > */ > -struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > - struct dentry *base, int len) > +struct dentry *lookup_one(struct mnt_idmap *idmap, struct qstr name, > + struct dentry *base) > { > struct dentry *dentry; > struct qstr this; > @@ -2942,7 +2940,7 @@ struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > > WARN_ON_ONCE(!inode_is_locked(base->d_inode)); > > - err = lookup_one_common(idmap, name, base, len, &this); > + err = lookup_one_common(idmap, name.name, base, name.len, &this); > if (err) > return ERR_PTR(err); > > @@ -2952,27 +2950,24 @@ struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > EXPORT_SYMBOL(lookup_one); > > /** > - * lookup_one_unlocked - filesystem helper to lookup single pathname component > + * lookup_one_unlocked - lookup single pathname component > * @idmap: idmap of the mount the lookup is performed from > - * @name: pathname component to lookup > + * @name: qstr olding pathname component to lookup > * @base: base directory to lookup from > - * @len: maximum length @len should be interpreted to > * > - * Note that this routine is purely a helper for filesystem usage and should > - * not be called by generic code. > + * This can be used for in-kernel filesystem clients such as file servers. > * > * Unlike lookup_one_len, it should be called without the parent > - * i_mutex held, and will take the i_mutex itself if necessary. > + * i_rwsem held, and will take the i_rwsem itself if necessary. > */ > struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, > - const char *name, struct dentry *base, > - int len) > + struct qstr name, struct dentry *base) > { > struct qstr this; > int err; > struct dentry *ret; > > - err = lookup_one_common(idmap, name, base, len, &this); > + err = lookup_one_common(idmap, name.name, base, name.len, &this); > if (err) > return ERR_PTR(err); > > @@ -2984,12 +2979,10 @@ struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, > EXPORT_SYMBOL(lookup_one_unlocked); > > /** > - * lookup_one_positive_unlocked - filesystem helper to lookup single > - * pathname component > + * lookup_one_positive_unlocked - lookup single pathname component > * @idmap: idmap of the mount the lookup is performed from > - * @name: pathname component to lookup > + * @name: qstr holding pathname component to lookup > * @base: base directory to lookup from > - * @len: maximum length @len should be interpreted to > * > * This helper will yield ERR_PTR(-ENOENT) on negatives. The helper returns > * known positive or ERR_PTR(). This is what most of the users want. > @@ -2998,16 +2991,15 @@ EXPORT_SYMBOL(lookup_one_unlocked); > * time, so callers of lookup_one_unlocked() need to be very careful; pinned > * positives have >d_inode stable, so this one avoids such problems. > * > - * Note that this routine is purely a helper for filesystem usage and should > - * not be called by generic code. > + * This can be used for in-kernel filesystem clients such as file servers. > * > - * The helper should be called without i_mutex held. > + * The helper should be called without i_rwsem held. > */ > struct dentry *lookup_one_positive_unlocked(struct mnt_idmap *idmap, > - const char *name, > - struct dentry *base, int len) > + struct qstr name, > + struct dentry *base) > { > - struct dentry *ret = lookup_one_unlocked(idmap, name, base, len); > + struct dentry *ret = lookup_one_unlocked(idmap, name, base); > > if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) { > dput(ret); > @@ -3032,7 +3024,7 @@ EXPORT_SYMBOL(lookup_one_positive_unlocked); > struct dentry *lookup_one_len_unlocked(const char *name, > struct dentry *base, int len) > { > - return lookup_one_unlocked(&nop_mnt_idmap, name, base, len); > + return lookup_one_unlocked(&nop_mnt_idmap, QSTR_LEN(name, len), base); > } > EXPORT_SYMBOL(lookup_one_len_unlocked); > > @@ -3047,7 +3039,8 @@ EXPORT_SYMBOL(lookup_one_len_unlocked); > struct dentry *lookup_positive_unlocked(const char *name, > struct dentry *base, int len) > { > - return lookup_one_positive_unlocked(&nop_mnt_idmap, name, base, len); > + return lookup_one_positive_unlocked(&nop_mnt_idmap, QSTR_LEN(name, len), > + base); > } > EXPORT_SYMBOL(lookup_positive_unlocked); > > diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c > index be5c65d6f848..6a6301e4bba5 100644 > --- a/fs/overlayfs/namei.c > +++ b/fs/overlayfs/namei.c > @@ -205,8 +205,8 @@ static struct dentry *ovl_lookup_positive_unlocked(struct ovl_lookup_data *d, > struct dentry *base, int len, > bool drop_negative) > { > - struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->layer->mnt), name, > - base, len); > + struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->layer->mnt), > + QSTR_LEN(name, len), base); > > if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) { > if (drop_negative && ret->d_lockref.count == 1) { > @@ -789,8 +789,8 @@ struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper, > if (err) > return ERR_PTR(err); > > - index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), name.name, > - ofs->workdir, name.len); > + index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), name, > + ofs->workdir); > if (IS_ERR(index)) { > err = PTR_ERR(index); > if (err == -ENOENT) { > @@ -1396,7 +1396,7 @@ bool ovl_lower_positive(struct dentry *dentry) > > this = lookup_one_positive_unlocked( > mnt_idmap(parentpath->layer->mnt), > - name->name, parentpath->dentry, name->len); > + *name, parentpath->dentry); > if (IS_ERR(this)) { > switch (PTR_ERR(this)) { > case -ENOENT: > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h > index 6f2f8f4cfbbc..ceaf4eb199c7 100644 > --- a/fs/overlayfs/overlayfs.h > +++ b/fs/overlayfs/overlayfs.h > @@ -402,7 +402,7 @@ static inline struct dentry *ovl_lookup_upper(struct ovl_fs *ofs, > const char *name, > struct dentry *base, int len) > { > - return lookup_one(ovl_upper_mnt_idmap(ofs), name, base, len); > + return lookup_one(ovl_upper_mnt_idmap(ofs), QSTR_LEN(name, len), base); > } > > static inline bool ovl_open_flags_need_copy_up(int flags) > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c > index 881ec5592da5..68df61f4bba7 100644 > --- a/fs/overlayfs/readdir.c > +++ b/fs/overlayfs/readdir.c > @@ -271,7 +271,6 @@ static bool ovl_fill_merge(struct dir_context *ctx, const char *name, > static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data *rdd) > { > int err; > - struct ovl_cache_entry *p; > struct dentry *dentry, *dir = path->dentry; > const struct cred *old_cred; > > @@ -280,9 +279,11 @@ static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data > err = down_write_killable(&dir->d_inode->i_rwsem); > if (!err) { > while (rdd->first_maybe_whiteout) { > - p = rdd->first_maybe_whiteout; > + struct ovl_cache_entry *p = > + rdd->first_maybe_whiteout; > rdd->first_maybe_whiteout = p->next_maybe_whiteout; > - dentry = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len); > + dentry = lookup_one(mnt_idmap(path->mnt), > + QSTR_LEN(p->name, p->len), dir); > if (!IS_ERR(dentry)) { > p->is_whiteout = ovl_is_whiteout(dentry); > dput(dentry); > @@ -492,7 +493,7 @@ static int ovl_cache_update(const struct path *path, struct ovl_cache_entry *p, > } > } > /* This checks also for xwhiteouts */ > - this = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len); > + this = lookup_one(mnt_idmap(path->mnt), QSTR_LEN(p->name, p->len), dir); > if (IS_ERR_OR_NULL(this) || !this->d_inode) { > /* Mark a stale entry */ > p->is_whiteout = true; > diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c > index f1efcd027475..c862e3bd4531 100644 > --- a/fs/smb/server/smb2pdu.c > +++ b/fs/smb/server/smb2pdu.c > @@ -4091,9 +4091,10 @@ static int process_query_dir_entries(struct smb2_query_dir_private *priv) > return -EINVAL; > > lock_dir(priv->dir_fp); > - dent = lookup_one(idmap, priv->d_info->name, > - priv->dir_fp->filp->f_path.dentry, > - priv->d_info->name_len); > + dent = lookup_one(idmap, > + QSTR_LEN(priv->d_info->name, > + priv->d_info->name_len), > + priv->dir_fp->filp->f_path.dentry); > unlock_dir(priv->dir_fp); > > if (IS_ERR(dent)) { > diff --git a/include/linux/dcache.h b/include/linux/dcache.h > index 45bff10d3773..1f01f4e734c5 100644 > --- a/include/linux/dcache.h > +++ b/include/linux/dcache.h > @@ -57,7 +57,8 @@ struct qstr { > }; > > #define QSTR_INIT(n,l) { { { .len = l } }, .name = n } > -#define QSTR(n) (struct qstr)QSTR_INIT(n, strlen(n)) > +#define QSTR_LEN(n,l) (struct qstr)QSTR_INIT(n,l) > +#define QSTR(n) QSTR_LEN(n, strlen(n)) > > extern const struct qstr empty_name; > extern const struct qstr slash_name; > diff --git a/include/linux/namei.h b/include/linux/namei.h > index e3042176cdf4..508dae67e3c5 100644 > --- a/include/linux/namei.h > +++ b/include/linux/namei.h > @@ -73,13 +73,12 @@ extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int); > extern struct dentry *lookup_one_len(const char *, struct dentry *, int); > extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int); > extern struct dentry *lookup_positive_unlocked(const char *, struct dentry *, int); > -struct dentry *lookup_one(struct mnt_idmap *, const char *, struct dentry *, int); > +struct dentry *lookup_one(struct mnt_idmap *, struct qstr, struct dentry *); > struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, > - const char *name, struct dentry *base, > - int len); > + struct qstr name, struct dentry *base); > struct dentry *lookup_one_positive_unlocked(struct mnt_idmap *idmap, > - const char *name, > - struct dentry *base, int len); > + struct qstr name, > + struct dentry *base); > > extern int follow_down_one(struct path *); > extern int follow_down(struct path *path, unsigned int flags); Reviewed-by: Jeff Layton <jlayton@kernel.org>
NeilBrown <neil@brown.name> wrote: > Also the path component name is passed as "name" and "len" which are > (confusingly?) separate by the "base". In some cases the len in simply > "strlen" and so passing a qstr using QSTR() would make the calling > clearer. > Other callers do pass separate name and len which are stored in a > struct. Sometimes these are already stored in a qstr, other times it > easily could be. > > So this patch changes these three functions to receive a 'struct qstr', > and improves the documentation. You did want 'struct qstr' not 'struct qstr *' right? I think there are arches where this will cause the compiler to skip a register argument or two if it's the second argument or third argument - i386 for example. Plus you have an 8-byte alignment requirement because of the u64 in it that may suck if passed through several layers of function. David
On Wed, Mar 19, 2025 at 02:01:32PM +1100, NeilBrown wrote: > -struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > - struct dentry *base, int len) > +struct dentry *lookup_one(struct mnt_idmap *idmap, struct qstr name, > + struct dentry *base) > { > struct dentry *dentry; > struct qstr this; > @@ -2942,7 +2940,7 @@ struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > > WARN_ON_ONCE(!inode_is_locked(base->d_inode)); > > - err = lookup_one_common(idmap, name, base, len, &this); > + err = lookup_one_common(idmap, name.name, base, name.len, &this); No. Just look at what lookup_one_common() is doing as the first step. this->name = name; this->len = len; You copy your argument's fields to corresponding fields of *&this. It might make sense to pass a qstr, but not like that - just pass a _pointer_ to struct qstr instead. Have lookup_one_common() do this: static int lookup_one_common(struct mnt_idmap *idmap, struct qstr *this, struct dentry *base) { const unsigned char *name = this->name; int len = this->len; if (!len) return -EACCES; this->hash = full_name_hash(base, name, len); if (is_dot_dotdot(name, len)) return -EACCES; while (len--) { unsigned int c = *name++; if (c == '/' || c == '\0') return -EACCES; } /* * See if the low-level filesystem might want * to use its own hash.. */ if (base->d_flags & DCACHE_OP_HASH) { int err = base->d_op->d_hash(base, this); if (err < 0) return err; } return inode_permission(idmap, base->d_inode, MAY_EXEC); } and adjust the callers; e.g. struct dentry *lookup_one(struct mnt_idmap *idmap, struct qstr *this, struct dentry *base) { struct dentry *dentry; int err; WARN_ON_ONCE(!inode_is_locked(base->d_inode)); err = lookup_one_common(idmap, this, base); if (err) return ERR_PTR(err); dentry = lookup_dcache(this, base, 0); return dentry ? dentry : __lookup_slow(this, base, 0); } with callers passing idmap, &QSTR_LEN(name, len), base instead of idmap, name, base, len. lookup_one_common() looks at the fields separately; its callers do not.
On Thu, Mar 20, 2025 at 02:04:49PM +0000, David Howells wrote: > NeilBrown <neil@brown.name> wrote: > > > Also the path component name is passed as "name" and "len" which are > > (confusingly?) separate by the "base". In some cases the len in simply > > "strlen" and so passing a qstr using QSTR() would make the calling > > clearer. > > Other callers do pass separate name and len which are stored in a > > struct. Sometimes these are already stored in a qstr, other times it > > easily could be. > > > > So this patch changes these three functions to receive a 'struct qstr', > > and improves the documentation. > > You did want 'struct qstr' not 'struct qstr *' right? I think there are > arches where this will cause the compiler to skip a register argument or two > if it's the second argument or third argument - i386 for example. Plus you > have an 8-byte alignment requirement because of the u64 in it that may suck if > passed through several layers of function. Not just that - you end up with *two* struct qstr instances for no good reason, copying from the one passed by value field-by-field into the other one, then passing the *address* of the copy to the functions that do actual work.
On Sat, 22 Mar 2025, Al Viro wrote: > On Wed, Mar 19, 2025 at 02:01:32PM +1100, NeilBrown wrote: > > > -struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > > - struct dentry *base, int len) > > +struct dentry *lookup_one(struct mnt_idmap *idmap, struct qstr name, > > + struct dentry *base) > > > { > > struct dentry *dentry; > > struct qstr this; > > @@ -2942,7 +2940,7 @@ struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, > > > > WARN_ON_ONCE(!inode_is_locked(base->d_inode)); > > > > - err = lookup_one_common(idmap, name, base, len, &this); > > + err = lookup_one_common(idmap, name.name, base, name.len, &this); > > No. Just look at what lookup_one_common() is doing as the first step. > > this->name = name; > this->len = len; This code is cleaned up in a later patch. lookup_one_common receives the address of just one qstr which is initialised with qstr that is passed in. So on x86_64, the original qstr is passed in as 2 registers. These are stored in the stack and the address is passed to lookup_noperm_common(), as lookup_one_common() gets inlined. We have to put the two values onto the stack at some point, either in the original callers, or in the lookup_one family of functions. I think it is cleaner in lookup_one as we don't need to put a & in front of all the QSTR calls. But we can change it to pass the pointer if you really think that is better. Thanks, NeilBrown > > You copy your argument's fields to corresponding fields of *&this. It might make > sense to pass a qstr, but not like that - just pass a _pointer_ to struct qstr instead. > > Have lookup_one_common() do this: > > static int lookup_one_common(struct mnt_idmap *idmap, > struct qstr *this, struct dentry *base) > { > const unsigned char *name = this->name; > int len = this->len; > if (!len) > return -EACCES; > > this->hash = full_name_hash(base, name, len); > if (is_dot_dotdot(name, len)) > return -EACCES; > > while (len--) { > unsigned int c = *name++; > if (c == '/' || c == '\0') > return -EACCES; > } > /* > * See if the low-level filesystem might want > * to use its own hash.. > */ > if (base->d_flags & DCACHE_OP_HASH) { > int err = base->d_op->d_hash(base, this); > if (err < 0) > return err; > } > > return inode_permission(idmap, base->d_inode, MAY_EXEC); > } > > and adjust the callers; e.g. > struct dentry *lookup_one(struct mnt_idmap *idmap, struct qstr *this, > struct dentry *base) > { > struct dentry *dentry; > int err; > > WARN_ON_ONCE(!inode_is_locked(base->d_inode)); > > err = lookup_one_common(idmap, this, base); > if (err) > return ERR_PTR(err); > > dentry = lookup_dcache(this, base, 0); > return dentry ? dentry : __lookup_slow(this, base, 0); > } > > with callers passing idmap, &QSTR_LEN(name, len), base instead of > idmap, name, base, len. lookup_one_common() looks at the fields > separately; its callers do not. >
On Fri, 21 Mar 2025, David Howells wrote: > NeilBrown <neil@brown.name> wrote: > > > Also the path component name is passed as "name" and "len" which are > > (confusingly?) separate by the "base". In some cases the len in simply > > "strlen" and so passing a qstr using QSTR() would make the calling > > clearer. > > Other callers do pass separate name and len which are stored in a > > struct. Sometimes these are already stored in a qstr, other times it > > easily could be. > > > > So this patch changes these three functions to receive a 'struct qstr', > > and improves the documentation. > > You did want 'struct qstr' not 'struct qstr *' right? I think there are > arches where this will cause the compiler to skip a register argument or two > if it's the second argument or third argument - i386 for example. Plus you > have an 8-byte alignment requirement because of the u64 in it that may suck if > passed through several layers of function. I don't think it is passed through several layers - except where the intermediate are inlined. And gcc enforces 16 byte alignment of the stack on function calls for i386, so I don't think alignment will be an issue. I thought 'struct qstr' would result in slightly cleaner calling. But I cannot make a strong argument in favour of it so I'm willing to change if there are concerns. Thanks, NeilBrown
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 6817614e0820..06296ffd1e81 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -1196,3 +1196,12 @@ should use d_drop();d_splice_alias() and return the result of the latter. If a positive dentry cannot be returned for some reason, in-kernel clients such as cachefiles, nfsd, smb/server may not perform ideally but will fail-safe. + +--- + +** mandatory** + +lookup_one(), lookup_one_unlocked(), lookup_one_positive_unlocked() now +take a qstr instead of a name and len. These, not the "one_len" +versions, should be used whenever accessing a filesystem from outside +that filesysmtem, through a mount point - which will have a mnt_idmap. diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 6c18bad53cd3..f94b638f9478 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -911,7 +911,7 @@ static noinline int btrfs_mksubvol(const struct path *parent, if (error == -EINTR) return error; - dentry = lookup_one(idmap, name, parent->dentry, namelen); + dentry = lookup_one(idmap, QSTR_LEN(name, namelen), parent->dentry); error = PTR_ERR(dentry); if (IS_ERR(dentry)) goto out_unlock; @@ -2289,7 +2289,6 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, struct btrfs_ioctl_vol_args_v2 *vol_args2 = NULL; struct mnt_idmap *idmap = file_mnt_idmap(file); char *subvol_name, *subvol_name_ptr = NULL; - int subvol_namelen; int ret = 0; bool destroy_parent = false; @@ -2412,10 +2411,8 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, goto out; } - subvol_namelen = strlen(subvol_name); - if (strchr(subvol_name, '/') || - strncmp(subvol_name, "..", subvol_namelen) == 0) { + strcmp(subvol_name, "..") == 0) { ret = -EINVAL; goto free_subvol_name; } @@ -2428,7 +2425,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, ret = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT); if (ret == -EINTR) goto free_subvol_name; - dentry = lookup_one(idmap, subvol_name, parent, subvol_namelen); + dentry = lookup_one(idmap, QSTR(subvol_name), parent); if (IS_ERR(dentry)) { ret = PTR_ERR(dentry); goto out_unlock_dir; diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c index 0c899cfba578..974b432087aa 100644 --- a/fs/exportfs/expfs.c +++ b/fs/exportfs/expfs.c @@ -145,7 +145,7 @@ static struct dentry *reconnect_one(struct vfsmount *mnt, if (err) goto out_err; dprintk("%s: found name: %s\n", __func__, nbuf); - tmp = lookup_one_unlocked(mnt_idmap(mnt), nbuf, parent, strlen(nbuf)); + tmp = lookup_one_unlocked(mnt_idmap(mnt), QSTR(nbuf), parent); if (IS_ERR(tmp)) { dprintk("lookup failed: %ld\n", PTR_ERR(tmp)); err = PTR_ERR(tmp); @@ -551,8 +551,7 @@ exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, } inode_lock(target_dir->d_inode); - nresult = lookup_one(mnt_idmap(mnt), nbuf, - target_dir, strlen(nbuf)); + nresult = lookup_one(mnt_idmap(mnt), QSTR(nbuf), target_dir); if (!IS_ERR(nresult)) { if (unlikely(nresult->d_inode != result->d_inode)) { dput(nresult); diff --git a/fs/namei.c b/fs/namei.c index b5abf456c5f4..75816fa80028 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2922,19 +2922,17 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) EXPORT_SYMBOL(lookup_one_len); /** - * lookup_one - filesystem helper to lookup single pathname component + * lookup_one - lookup single pathname component * @idmap: idmap of the mount the lookup is performed from - * @name: pathname component to lookup + * @name: qstr holding pathname component to lookup * @base: base directory to lookup from - * @len: maximum length @len should be interpreted to * - * Note that this routine is purely a helper for filesystem usage and should - * not be called by generic code. + * This can be used for in-kernel filesystem clients such as file servers. * * The caller must hold base->i_mutex. */ -struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, - struct dentry *base, int len) +struct dentry *lookup_one(struct mnt_idmap *idmap, struct qstr name, + struct dentry *base) { struct dentry *dentry; struct qstr this; @@ -2942,7 +2940,7 @@ struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, WARN_ON_ONCE(!inode_is_locked(base->d_inode)); - err = lookup_one_common(idmap, name, base, len, &this); + err = lookup_one_common(idmap, name.name, base, name.len, &this); if (err) return ERR_PTR(err); @@ -2952,27 +2950,24 @@ struct dentry *lookup_one(struct mnt_idmap *idmap, const char *name, EXPORT_SYMBOL(lookup_one); /** - * lookup_one_unlocked - filesystem helper to lookup single pathname component + * lookup_one_unlocked - lookup single pathname component * @idmap: idmap of the mount the lookup is performed from - * @name: pathname component to lookup + * @name: qstr olding pathname component to lookup * @base: base directory to lookup from - * @len: maximum length @len should be interpreted to * - * Note that this routine is purely a helper for filesystem usage and should - * not be called by generic code. + * This can be used for in-kernel filesystem clients such as file servers. * * Unlike lookup_one_len, it should be called without the parent - * i_mutex held, and will take the i_mutex itself if necessary. + * i_rwsem held, and will take the i_rwsem itself if necessary. */ struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, - const char *name, struct dentry *base, - int len) + struct qstr name, struct dentry *base) { struct qstr this; int err; struct dentry *ret; - err = lookup_one_common(idmap, name, base, len, &this); + err = lookup_one_common(idmap, name.name, base, name.len, &this); if (err) return ERR_PTR(err); @@ -2984,12 +2979,10 @@ struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, EXPORT_SYMBOL(lookup_one_unlocked); /** - * lookup_one_positive_unlocked - filesystem helper to lookup single - * pathname component + * lookup_one_positive_unlocked - lookup single pathname component * @idmap: idmap of the mount the lookup is performed from - * @name: pathname component to lookup + * @name: qstr holding pathname component to lookup * @base: base directory to lookup from - * @len: maximum length @len should be interpreted to * * This helper will yield ERR_PTR(-ENOENT) on negatives. The helper returns * known positive or ERR_PTR(). This is what most of the users want. @@ -2998,16 +2991,15 @@ EXPORT_SYMBOL(lookup_one_unlocked); * time, so callers of lookup_one_unlocked() need to be very careful; pinned * positives have >d_inode stable, so this one avoids such problems. * - * Note that this routine is purely a helper for filesystem usage and should - * not be called by generic code. + * This can be used for in-kernel filesystem clients such as file servers. * - * The helper should be called without i_mutex held. + * The helper should be called without i_rwsem held. */ struct dentry *lookup_one_positive_unlocked(struct mnt_idmap *idmap, - const char *name, - struct dentry *base, int len) + struct qstr name, + struct dentry *base) { - struct dentry *ret = lookup_one_unlocked(idmap, name, base, len); + struct dentry *ret = lookup_one_unlocked(idmap, name, base); if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) { dput(ret); @@ -3032,7 +3024,7 @@ EXPORT_SYMBOL(lookup_one_positive_unlocked); struct dentry *lookup_one_len_unlocked(const char *name, struct dentry *base, int len) { - return lookup_one_unlocked(&nop_mnt_idmap, name, base, len); + return lookup_one_unlocked(&nop_mnt_idmap, QSTR_LEN(name, len), base); } EXPORT_SYMBOL(lookup_one_len_unlocked); @@ -3047,7 +3039,8 @@ EXPORT_SYMBOL(lookup_one_len_unlocked); struct dentry *lookup_positive_unlocked(const char *name, struct dentry *base, int len) { - return lookup_one_positive_unlocked(&nop_mnt_idmap, name, base, len); + return lookup_one_positive_unlocked(&nop_mnt_idmap, QSTR_LEN(name, len), + base); } EXPORT_SYMBOL(lookup_positive_unlocked); diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c index be5c65d6f848..6a6301e4bba5 100644 --- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -205,8 +205,8 @@ static struct dentry *ovl_lookup_positive_unlocked(struct ovl_lookup_data *d, struct dentry *base, int len, bool drop_negative) { - struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->layer->mnt), name, - base, len); + struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->layer->mnt), + QSTR_LEN(name, len), base); if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) { if (drop_negative && ret->d_lockref.count == 1) { @@ -789,8 +789,8 @@ struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper, if (err) return ERR_PTR(err); - index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), name.name, - ofs->workdir, name.len); + index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), name, + ofs->workdir); if (IS_ERR(index)) { err = PTR_ERR(index); if (err == -ENOENT) { @@ -1396,7 +1396,7 @@ bool ovl_lower_positive(struct dentry *dentry) this = lookup_one_positive_unlocked( mnt_idmap(parentpath->layer->mnt), - name->name, parentpath->dentry, name->len); + *name, parentpath->dentry); if (IS_ERR(this)) { switch (PTR_ERR(this)) { case -ENOENT: diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index 6f2f8f4cfbbc..ceaf4eb199c7 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -402,7 +402,7 @@ static inline struct dentry *ovl_lookup_upper(struct ovl_fs *ofs, const char *name, struct dentry *base, int len) { - return lookup_one(ovl_upper_mnt_idmap(ofs), name, base, len); + return lookup_one(ovl_upper_mnt_idmap(ofs), QSTR_LEN(name, len), base); } static inline bool ovl_open_flags_need_copy_up(int flags) diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index 881ec5592da5..68df61f4bba7 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -271,7 +271,6 @@ static bool ovl_fill_merge(struct dir_context *ctx, const char *name, static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data *rdd) { int err; - struct ovl_cache_entry *p; struct dentry *dentry, *dir = path->dentry; const struct cred *old_cred; @@ -280,9 +279,11 @@ static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data err = down_write_killable(&dir->d_inode->i_rwsem); if (!err) { while (rdd->first_maybe_whiteout) { - p = rdd->first_maybe_whiteout; + struct ovl_cache_entry *p = + rdd->first_maybe_whiteout; rdd->first_maybe_whiteout = p->next_maybe_whiteout; - dentry = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len); + dentry = lookup_one(mnt_idmap(path->mnt), + QSTR_LEN(p->name, p->len), dir); if (!IS_ERR(dentry)) { p->is_whiteout = ovl_is_whiteout(dentry); dput(dentry); @@ -492,7 +493,7 @@ static int ovl_cache_update(const struct path *path, struct ovl_cache_entry *p, } } /* This checks also for xwhiteouts */ - this = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len); + this = lookup_one(mnt_idmap(path->mnt), QSTR_LEN(p->name, p->len), dir); if (IS_ERR_OR_NULL(this) || !this->d_inode) { /* Mark a stale entry */ p->is_whiteout = true; diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index f1efcd027475..c862e3bd4531 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -4091,9 +4091,10 @@ static int process_query_dir_entries(struct smb2_query_dir_private *priv) return -EINVAL; lock_dir(priv->dir_fp); - dent = lookup_one(idmap, priv->d_info->name, - priv->dir_fp->filp->f_path.dentry, - priv->d_info->name_len); + dent = lookup_one(idmap, + QSTR_LEN(priv->d_info->name, + priv->d_info->name_len), + priv->dir_fp->filp->f_path.dentry); unlock_dir(priv->dir_fp); if (IS_ERR(dent)) { diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 45bff10d3773..1f01f4e734c5 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -57,7 +57,8 @@ struct qstr { }; #define QSTR_INIT(n,l) { { { .len = l } }, .name = n } -#define QSTR(n) (struct qstr)QSTR_INIT(n, strlen(n)) +#define QSTR_LEN(n,l) (struct qstr)QSTR_INIT(n,l) +#define QSTR(n) QSTR_LEN(n, strlen(n)) extern const struct qstr empty_name; extern const struct qstr slash_name; diff --git a/include/linux/namei.h b/include/linux/namei.h index e3042176cdf4..508dae67e3c5 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -73,13 +73,12 @@ extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int); extern struct dentry *lookup_one_len(const char *, struct dentry *, int); extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int); extern struct dentry *lookup_positive_unlocked(const char *, struct dentry *, int); -struct dentry *lookup_one(struct mnt_idmap *, const char *, struct dentry *, int); +struct dentry *lookup_one(struct mnt_idmap *, struct qstr, struct dentry *); struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, - const char *name, struct dentry *base, - int len); + struct qstr name, struct dentry *base); struct dentry *lookup_one_positive_unlocked(struct mnt_idmap *idmap, - const char *name, - struct dentry *base, int len); + struct qstr name, + struct dentry *base); extern int follow_down_one(struct path *); extern int follow_down(struct path *path, unsigned int flags);
The family of functions: lookup_one() lookup_one_unlocked() lookup_one_positive_unlocked() appear designed to be used by external clients of the filesystem rather than by filesystems acting on themselves as the lookup_one_len family are used. They are used by: btrfs/ioctl - which is a user-space interface rather than an internal activity exportfs - i.e. from nfsd or the open_by_handle_at interface overlayfs - at access the underlying filesystems smb/server - for file service They should be used by nfsd (more than just the exportfs path) and cachefs but aren't. It would help if the documentation didn't claim they should "not be called by generic code". Also the path component name is passed as "name" and "len" which are (confusingly?) separate by the "base". In some cases the len in simply "strlen" and so passing a qstr using QSTR() would make the calling clearer. Other callers do pass separate name and len which are stored in a struct. Sometimes these are already stored in a qstr, other times it easily could be. So this patch changes these three functions to receive a 'struct qstr', and improves the documentation. QSTR_LEN() is added to make it easy to pass a QSTR containing a known len. Signed-off-by: NeilBrown <neil@brown.name> --- Documentation/filesystems/porting.rst | 9 +++++ fs/btrfs/ioctl.c | 9 ++--- fs/exportfs/expfs.c | 5 ++- fs/namei.c | 51 ++++++++++++--------------- fs/overlayfs/namei.c | 10 +++--- fs/overlayfs/overlayfs.h | 2 +- fs/overlayfs/readdir.c | 9 ++--- fs/smb/server/smb2pdu.c | 7 ++-- include/linux/dcache.h | 3 +- include/linux/namei.h | 9 +++-- 10 files changed, 57 insertions(+), 57 deletions(-)