On Tue, May 12, 2020 at 11:32 AM Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>
> On Tue, May 12, 2020 at 10:50:31AM +0300, Amir Goldstein wrote:
>
> > This helper should be in vfs code, not duplicating vfs code
> > and please don't duplicate code in vfs either.
> >
> > I think you can use a lookup flag (LOOKUP_POSITIVE_CACHE???)
> > to describe the desired behavior and implement it inside
> > lookup_slow(). Document the semantics as well as explain
> > in the context of the helper the cases where modules might
> > find this useful (because they have higher level caches).
> >
> > Besides the fact that this helper really needs review by Al
> > and that duplicating subtle code is wrong in so many levels,
> > I suppose the functionality could prove useful to other subsystems
> > as well.
>
> Something like this (untested). Needs splitup and changelogs.
>
> Thanks,
> Miklos
>
> ---
> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> index c31f362fa098..e52a3b35ebac 100644
> --- a/fs/cifs/cifsfs.c
> +++ b/fs/cifs/cifsfs.c
> @@ -752,7 +752,7 @@ cifs_get_root(struct smb_vol *vol, struct super_block *sb)
> while (*s && *s != sep)
> s++;
>
> - child = lookup_positive_unlocked(p, dentry, s - p);
> + child = lookup_positive_unlocked(p, dentry, s - p, 0);
> dput(dentry);
> dentry = child;
> } while (!IS_ERR(dentry));
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index b7f2e971ecbc..df4f37a6a9ab 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -299,7 +299,7 @@ struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
> if (!parent)
> parent = debugfs_mount->mnt_root;
>
> - dentry = lookup_positive_unlocked(name, parent, strlen(name));
> + dentry = lookup_positive_unlocked(name, parent, strlen(name), 0);
> if (IS_ERR(dentry))
> return NULL;
> return dentry;
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index e23752d9a79f..e39af6313ad9 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -407,7 +407,7 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
> name = encrypted_and_encoded_name;
> }
>
> - lower_dentry = lookup_one_len_unlocked(name, lower_dir_dentry, len);
> + lower_dentry = lookup_one_len_unlocked(name, lower_dir_dentry, len, 0);
> if (IS_ERR(lower_dentry)) {
> ecryptfs_printk(KERN_DEBUG, "%s: lookup_one_len() returned "
> "[%ld] on lower_dentry = [%s]\n", __func__,
> diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
> index 2dd55b172d57..a4276d14aebb 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_len_unlocked(nbuf, parent, strlen(nbuf));
> + tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf), 0);
> if (IS_ERR(tmp)) {
> dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
> err = PTR_ERR(tmp);
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index 9dc7e7a64e10..92e7f264baa1 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -224,7 +224,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
> return ERR_PTR(-EINVAL);
> }
> dtmp = lookup_positive_unlocked(kntmp->name, dentry,
> - strlen(kntmp->name));
> + strlen(kntmp->name), 0);
> dput(dentry);
> if (IS_ERR(dtmp))
> return dtmp;
> diff --git a/fs/namei.c b/fs/namei.c
> index a320371899cf..e70b7a14bdcc 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1532,6 +1532,9 @@ static struct dentry *__lookup_slow(const struct qstr *name,
> if (unlikely(old)) {
> dput(dentry);
> dentry = old;
> + } else if ((flags & LOOKUP_NO_NEGATIVE) &&
> + d_is_negative(dentry)) {
> + d_drop(dentry);
> }
> }
> return dentry;
> @@ -2562,7 +2565,8 @@ EXPORT_SYMBOL(lookup_one_len);
> * i_mutex held, and will take the i_mutex itself if necessary.
> */
> struct dentry *lookup_one_len_unlocked(const char *name,
> - struct dentry *base, int len)
> + struct dentry *base, int len,
> + unsigned int flags)
> {
> struct qstr this;
> int err;
> @@ -2572,9 +2576,9 @@ struct dentry *lookup_one_len_unlocked(const char *name,
> if (err)
> return ERR_PTR(err);
>
> - ret = lookup_dcache(&this, base, 0);
> + ret = lookup_dcache(&this, base, flags);
> if (!ret)
> - ret = lookup_slow(&this, base, 0);
> + ret = lookup_slow(&this, base, flags);
> return ret;
> }
> EXPORT_SYMBOL(lookup_one_len_unlocked);
> @@ -2588,9 +2592,10 @@ EXPORT_SYMBOL(lookup_one_len_unlocked);
> * this one avoids such problems.
> */
> struct dentry *lookup_positive_unlocked(const char *name,
> - struct dentry *base, int len)
> + struct dentry *base, int len,
> + unsigned int flags)
> {
> - struct dentry *ret = lookup_one_len_unlocked(name, base, len);
> + struct dentry *ret = lookup_one_len_unlocked(name, base, len, flags);
> if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
> dput(ret);
> ret = ERR_PTR(-ENOENT);
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index aae514d40b64..19628922969c 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -855,7 +855,7 @@ compose_entry_fh(struct nfsd3_readdirres *cd, struct svc_fh *fhp,
> } else
> dchild = dget(dparent);
> } else
> - dchild = lookup_positive_unlocked(name, dparent, namlen);
> + dchild = lookup_positive_unlocked(name, dparent, namlen, 0);
> if (IS_ERR(dchild))
> return rv;
> if (d_mountpoint(dchild))
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index 996ac01ee977..0c3c7928a319 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -3066,7 +3066,7 @@ nfsd4_encode_dirent_fattr(struct xdr_stream *xdr, struct nfsd4_readdir *cd,
> __be32 nfserr;
> int ignore_crossmnt = 0;
>
> - dentry = lookup_positive_unlocked(name, cd->rd_fhp->fh_dentry, namlen);
> + dentry = lookup_positive_unlocked(name, cd->rd_fhp->fh_dentry, namlen, 0);
> if (IS_ERR(dentry))
> return nfserrno(PTR_ERR(dentry));
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 0db23baf98e7..193857487060 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -200,7 +200,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> int err;
> bool last_element = !post[0];
>
> - this = lookup_positive_unlocked(name, base, namelen);
> + this = lookup_positive_unlocked(name, base, namelen,
> + LOOKUP_NO_NEGATIVE);
> if (IS_ERR(this)) {
> err = PTR_ERR(this);
> this = NULL;
> @@ -657,7 +658,7 @@ struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
> if (err)
> return ERR_PTR(err);
>
> - index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len);
> + index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len, 0);
> kfree(name.name);
> if (IS_ERR(index)) {
> if (PTR_ERR(index) == -ENOENT)
> @@ -689,7 +690,7 @@ struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
> if (err)
> return ERR_PTR(err);
>
> - index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len);
> + index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len, 0);
> if (IS_ERR(index)) {
> err = PTR_ERR(index);
> if (err == -ENOENT) {
> @@ -1137,7 +1138,7 @@ bool ovl_lower_positive(struct dentry *dentry)
> struct dentry *lowerdir = poe->lowerstack[i].dentry;
>
> this = lookup_positive_unlocked(name->name, lowerdir,
> - name->len);
> + name->len, 0);
> if (IS_ERR(this)) {
> switch (PTR_ERR(this)) {
> case -ENOENT:
> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> index b6a4f692d345..f588839ebe2e 100644
> --- a/fs/quota/dquot.c
> +++ b/fs/quota/dquot.c
> @@ -2488,7 +2488,7 @@ int dquot_quota_on_mount(struct super_block *sb, char *qf_name,
> struct dentry *dentry;
> int error;
>
> - dentry = lookup_positive_unlocked(qf_name, sb->s_root, strlen(qf_name));
> + dentry = lookup_positive_unlocked(qf_name, sb->s_root, strlen(qf_name), 0);
> if (IS_ERR(dentry))
> return PTR_ERR(dentry);
>
> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index a4bb992623c4..4896eeeeea46 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -49,6 +49,8 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT};
> /* LOOKUP_* flags which do scope-related checks based on the dirfd. */
> #define LOOKUP_IS_SCOPED (LOOKUP_BENEATH | LOOKUP_IN_ROOT)
>
> +#define LOOKUP_NO_NEGATIVE 0x200000 /* Hint: don't cache negative */
> +
The language lawyers will call this double negative, but I do
prefer this over LOOKUP_POSITIVE :-)
Thanks,
Amir.
