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smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=krisman.be; spf=pass smtp.mailfrom=krisman.be; dkim=pass (2048-bit key) header.d=krisman.be header.i=@krisman.be header.b=LXmHeZts; arc=none smtp.client-ip=217.70.183.196 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=krisman.be Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=krisman.be Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=krisman.be header.i=@krisman.be header.b="LXmHeZts" Received: by mail.gandi.net (Postfix) with ESMTPSA id ECAB743B89; Mon, 25 Aug 2025 17:11:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=krisman.be; s=gm1; t=1756141904; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VMo2y2Ps82gDSLjiJPHhyCa90JmOJ2n5TM25aj/Um84=; b=LXmHeZtsK8wr4K/IiyAn4SJAPa+uL8uoMIgmAsc0F33AvLWNloGLIwEsygD0+sqUkpwSe+ Rg5GuWcJv9WiGkuOy0YAftHc+/HjtrDctl01bljVpsTL785cJjAIvqXzhBbpVUweeHm+W4 /p4NUM29sRCZy3LSvqhGnYm/n5d02LdoKc2GW/JG55mMw/8pojNzFlZKnk+HxIb6P/3syJ +IeDRf10Vb1B8AdrzMn/tb29NR7jGzuwZfxNMi93JufAJwcOCoXHtra/GiCwxYnKtKs1AW uAeUE211DATSt4tL5u/Xa26mD2iXbdZnJJOyhQjxEC6WTLl6YYM3v7Dcuu59dw== From: Gabriel Krisman Bertazi To: Amir Goldstein Cc: =?utf-8?Q?Andr=C3=A9?= Almeida , Miklos Szeredi , Theodore Tso , linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alexander Viro , Christian Brauner , Jan Kara , kernel-dev@igalia.com Subject: Re: [PATCH v6 4/9] ovl: Create ovl_casefold() to support casefolded strncmp() In-Reply-To: (Amir Goldstein's message of "Mon, 25 Aug 2025 17:45:40 +0200") References: <20250822-tonyk-overlayfs-v6-0-8b6e9e604fa2@igalia.com> <20250822-tonyk-overlayfs-v6-4-8b6e9e604fa2@igalia.com> <875xeb64ks.fsf@mailhost.krisman.be> Date: Mon, 25 Aug 2025 13:11:40 -0400 Message-ID: <871poz4983.fsf@mailhost.krisman.be> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtdefgddujedvleehucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuifetpfffkfdpucggtfgfnhhsuhgsshgtrhhisggvnecuuegrihhlohhuthemuceftddunecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefhvfevufgjfhffkfgfgggtgfesthhqredttderjeenucfhrhhomhepifgrsghrihgvlhcumfhrihhsmhgrnhcuuegvrhhtrgiiihcuoehgrggsrhhivghlsehkrhhishhmrghnrdgsvgeqnecuggftrfgrthhtvghrnhepfedtvdehffevtddujeffffejudeuuefgvdeujeduhedtgfehkeefheegjefgueeknecukfhppeejtddrkedvrddukedvrdeikeenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepihhnvghtpeejtddrkedvrddukedvrdeikedphhgvlhhopehlohgtrghlhhhoshhtpdhmrghilhhfrhhomhepghgrsghrihgvlheskhhrihhsmhgrnhdrsggvpdhnsggprhgtphhtthhopeduuddprhgtphhtthhopegrmhhirhejfehilhesghhmrghilhdrtghomhdprhgtphhtthhopegrnhgurhgvrghlmhgvihgusehighgrlhhirgdrtghomhdprhgtphhtthhopehmihhklhhoshesshiivghrvgguihdrhhhupdhrtghpthhtohepthihthhsohesmhhithdrvgguuhdprhgtphhtthhopehlihhnuhigqdhunhhiohhnfhhssehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtoheplhhinhhugidqkhgvr hhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtoheplhhinhhugidqfhhsuggvvhgvlhesvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehvihhrohesiigvnhhivhdrlhhinhhugidrohhrghdruhhk X-GND-Sasl: gabriel@krisman.be Amir Goldstein writes: > On Mon, Aug 25, 2025 at 5:27=E2=80=AFPM Amir Goldstein wrote: >> >> On Mon, Aug 25, 2025 at 1:09=E2=80=AFPM Gabriel Krisman Bertazi >> wrote: >> > >> > Andr=C3=A9 Almeida writes: >> > >> > > To add overlayfs support casefold layers, create a new function >> > > ovl_casefold(), to be able to do case-insensitive strncmp(). >> > > >> > > ovl_casefold() allocates a new buffer and stores the casefolded vers= ion >> > > of the string on it. If the allocation or the casefold operation fai= ls, >> > > fallback to use the original string. >> > > >> > > The case-insentive name is then used in the rb-tree search/insertion >> > > operation. If the name is found in the rb-tree, the name can be >> > > discarded and the buffer is freed. If the name isn't found, it's then >> > > stored at struct ovl_cache_entry to be used later. >> > > >> > > Reviewed-by: Amir Goldstein >> > > Signed-off-by: Andr=C3=A9 Almeida >> > > --- >> > > Changes from v6: >> > > - Last version was using `strncmp(... tmp->len)` which was causing >> > > regressions. It should be `strncmp(... len)`. >> > > - Rename cf_len to c_len >> > > - Use c_len for tree operation: (cmp < 0 || len < tmp->c_len) >> > > - Remove needless kfree(cf_name) >> > > --- >> > > fs/overlayfs/readdir.c | 113 ++++++++++++++++++++++++++++++++++++++= ++--------- >> > > 1 file changed, 94 insertions(+), 19 deletions(-) >> > > >> > > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c >> > > index b65cdfce31ce27172d28d879559f1008b9c87320..dfc661b7bc3f87efbf14= 991e97cee169400d823b 100644 >> > > --- a/fs/overlayfs/readdir.c >> > > +++ b/fs/overlayfs/readdir.c >> > > @@ -27,6 +27,8 @@ struct ovl_cache_entry { >> > > bool is_upper; >> > > bool is_whiteout; >> > > bool check_xwhiteout; >> > > + const char *c_name; >> > > + int c_len; >> > > char name[]; >> > > }; >> > > >> > > @@ -45,6 +47,7 @@ struct ovl_readdir_data { >> > > struct list_head *list; >> > > struct list_head middle; >> > > struct ovl_cache_entry *first_maybe_whiteout; >> > > + struct unicode_map *map; >> > > int count; >> > > int err; >> > > bool is_upper; >> > > @@ -66,6 +69,27 @@ static struct ovl_cache_entry *ovl_cache_entry_fr= om_node(struct rb_node *n) >> > > return rb_entry(n, struct ovl_cache_entry, node); >> > > } >> > > >> > > +static int ovl_casefold(struct unicode_map *map, const char *str, i= nt len, char **dst) >> > > +{ >> > > + const struct qstr qstr =3D { .name =3D str, .len =3D len }; >> > > + int cf_len; >> > > + >> > > + if (!IS_ENABLED(CONFIG_UNICODE) || !map || is_dot_dotdot(str, = len)) >> > > + return 0; >> > > + >> > > + *dst =3D kmalloc(NAME_MAX, GFP_KERNEL); >> > > + >> > > + if (dst) { >> > > + cf_len =3D utf8_casefold(map, &qstr, *dst, NAME_MAX); >> > > + >> > > + if (cf_len > 0) >> > > + return cf_len; >> > > + } >> > > + >> > > + kfree(*dst); >> > > + return 0; >> > > +} >> > >> > Hi, >> > >> > I should just note this does not differentiates allocation errors from >> > casefolding errors (invalid encoding). It might be just a theoretical >> > error because GFP_KERNEL shouldn't fail (wink, wink) and the rest of t= he >> > operation is likely to fail too, but if you have an allocation failure= , you >> > can end up with an inconsistent cache, because a file is added under t= he >> > !casefolded name and a later successful lookup will look for the >> > casefolded version. >> >> Good point. >> I will fix this in my tree. > > wait why should we not fail to fill the cache for both allocation > and encoding errors? > We shouldn't fail the cache for encoding errors, just for allocation errors. Perhaps I am misreading the code, so please correct me if I'm wrong. if ovl_casefold fails, the non-casefolded name is used in the cache. That makes sense if the reason utf8_casefold failed is because the string cannot be casefolded (i.e. an invalid utf-8 string). For those strings, everything is fine. But on an allocation failure, the string might have a real casefolded version. If we fallback to the original string as the key, a cache lookup won't find the entry, since we compare with memcmp. > >> >> > >> > > + >> > > static bool ovl_cache_entry_find_link(const char *name, int len, >> > > struct rb_node ***link, >> > > struct rb_node **parent) >> > > @@ -79,10 +103,10 @@ static bool ovl_cache_entry_find_link(const cha= r *name, int len, >> > > >> > > *parent =3D *newp; >> > > tmp =3D ovl_cache_entry_from_node(*newp); >> > > - cmp =3D strncmp(name, tmp->name, len); >> > > + cmp =3D strncmp(name, tmp->c_name, len); >> > > if (cmp > 0) >> > > newp =3D &tmp->node.rb_right; >> > > - else if (cmp < 0 || len < tmp->len) >> > > + else if (cmp < 0 || len < tmp->c_len) >> > > newp =3D &tmp->node.rb_left; >> > > else >> > > found =3D true; >> > > @@ -101,10 +125,10 @@ static struct ovl_cache_entry *ovl_cache_entry= _find(struct rb_root *root, >> > > while (node) { >> > > struct ovl_cache_entry *p =3D ovl_cache_entry_from_nod= e(node); >> > > >> > > - cmp =3D strncmp(name, p->name, len); >> > > + cmp =3D strncmp(name, p->c_name, len); >> > > if (cmp > 0) >> > > node =3D p->node.rb_right; >> > > - else if (cmp < 0 || len < p->len) >> > > + else if (cmp < 0 || len < p->c_len) >> > > node =3D p->node.rb_left; >> > > else >> > > return p; >> > > @@ -145,6 +169,7 @@ static bool ovl_calc_d_ino(struct ovl_readdir_da= ta *rdd, >> > > >> > > static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readd= ir_data *rdd, >> > > const char *name, i= nt len, >> > > + const char *c_name,= int c_len, >> > > u64 ino, unsigned i= nt d_type) >> > > { >> > > struct ovl_cache_entry *p; >> > > @@ -167,6 +192,14 @@ static struct ovl_cache_entry *ovl_cache_entry_= new(struct ovl_readdir_data *rdd, >> > > /* Defer check for overlay.whiteout to ovl_iterate() */ >> > > p->check_xwhiteout =3D rdd->in_xwhiteouts_dir && d_type =3D=3D= DT_REG; >> > > >> > > + if (c_name && c_name !=3D name) { >> > > + p->c_name =3D c_name; >> > > + p->c_len =3D c_len; >> > > + } else { >> > > + p->c_name =3D p->name; >> > > + p->c_len =3D len; >> > > + } >> > > + >> > > if (d_type =3D=3D DT_CHR) { >> > > p->next_maybe_whiteout =3D rdd->first_maybe_whiteout; >> > > rdd->first_maybe_whiteout =3D p; >> > > @@ -174,48 +207,55 @@ static struct ovl_cache_entry *ovl_cache_entry= _new(struct ovl_readdir_data *rdd, >> > > return p; >> > > } >> > > >> > > -static bool ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd, >> > > - const char *name, int len, u64 ino, >> > > +/* Return 0 for found, 1 for added, <0 for error */ >> > > +static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd, >> > > + const char *name, int len, >> > > + const char *c_name, int c_len, >> > > + u64 ino, >> > > unsigned int d_type) >> > > { >> > > struct rb_node **newp =3D &rdd->root->rb_node; >> > > struct rb_node *parent =3D NULL; >> > > struct ovl_cache_entry *p; >> > > >> > > - if (ovl_cache_entry_find_link(name, len, &newp, &parent)) >> > > - return true; >> > > + if (ovl_cache_entry_find_link(c_name, c_len, &newp, &parent)) >> > > + return 0; >> > > >> > > - p =3D ovl_cache_entry_new(rdd, name, len, ino, d_type); >> > > + p =3D ovl_cache_entry_new(rdd, name, len, c_name, c_len, ino, = d_type); >> > > if (p =3D=3D NULL) { >> > > rdd->err =3D -ENOMEM; >> > > - return false; >> > > + return -ENOMEM; >> > > } >> > > >> > > list_add_tail(&p->l_node, rdd->list); >> > > rb_link_node(&p->node, parent, newp); >> > > rb_insert_color(&p->node, rdd->root); >> > > >> > > - return true; >> > > + return 1; >> > > } >> > > >> > > -static bool ovl_fill_lowest(struct ovl_readdir_data *rdd, >> > > +/* Return 0 for found, 1 for added, <0 for error */ >> > > +static int ovl_fill_lowest(struct ovl_readdir_data *rdd, >> > > const char *name, int namelen, >> > > + const char *c_name, int c_len, >> > > loff_t offset, u64 ino, unsigned int d_type) >> > > { >> > > struct ovl_cache_entry *p; >> > > >> > > - p =3D ovl_cache_entry_find(rdd->root, name, namelen); >> > > + p =3D ovl_cache_entry_find(rdd->root, c_name, c_len); >> > > if (p) { >> > > list_move_tail(&p->l_node, &rdd->middle); >> > > + return 0; >> > > } else { >> > > - p =3D ovl_cache_entry_new(rdd, name, namelen, ino, d_t= ype); >> > > + p =3D ovl_cache_entry_new(rdd, name, namelen, c_name, = c_len, >> > > + ino, d_type); >> > > if (p =3D=3D NULL) >> > > rdd->err =3D -ENOMEM; >> > > else >> > > list_add_tail(&p->l_node, &rdd->middle); >> > > } >> > > >> > > - return rdd->err =3D=3D 0; >> > > + return rdd->err ?: 1; >> > > } >> > > >> > > void ovl_cache_free(struct list_head *list) >> > > @@ -223,8 +263,11 @@ void ovl_cache_free(struct list_head *list) >> > > struct ovl_cache_entry *p; >> > > struct ovl_cache_entry *n; >> > > >> > > - list_for_each_entry_safe(p, n, list, l_node) >> > > + list_for_each_entry_safe(p, n, list, l_node) { >> > > + if (p->c_name !=3D p->name) >> > > + kfree(p->c_name); >> > > kfree(p); >> > > + } >> > > >> > > INIT_LIST_HEAD(list); >> > > } >> > > @@ -260,12 +303,36 @@ static bool ovl_fill_merge(struct dir_context = *ctx, const char *name, >> > > { >> > > struct ovl_readdir_data *rdd =3D >> > > container_of(ctx, struct ovl_readdir_data, ctx); >> > > + struct ovl_fs *ofs =3D OVL_FS(rdd->dentry->d_sb); >> > > + const char *c_name =3D NULL; >> > > + char *cf_name =3D NULL; >> > > + int c_len =3D 0, ret; >> > > + >> > > + if (ofs->casefold) >> > > + c_len =3D ovl_casefold(rdd->map, name, namelen, &cf_na= me); >> > > + >> > > + if (c_len <=3D 0) { >> > > + c_name =3D name; >> > > + c_len =3D namelen; >> > > + } else { >> > > + c_name =3D cf_name; >> > > + } >> > > >> > > rdd->count++; >> > > if (!rdd->is_lowest) >> > > - return ovl_cache_entry_add_rb(rdd, name, namelen, ino,= d_type); >> > > + ret =3D ovl_cache_entry_add_rb(rdd, name, namelen, c_n= ame, c_len, ino, d_type); >> > > else >> > > - return ovl_fill_lowest(rdd, name, namelen, offset, ino= , d_type); >> > > + ret =3D ovl_fill_lowest(rdd, name, namelen, c_name, c_= len, offset, ino, d_type); >> > > + >> > > + /* >> > > + * If ret =3D=3D 1, that means that c_name is being used as pa= rt of struct >> > > + * ovl_cache_entry and will be freed at ovl_cache_free(). Othe= rwise, >> > > + * c_name was found in the rb-tree so we can free it here. >> > > + */ >> > > + if (ret !=3D 1 && c_name !=3D name) >> > > + kfree(c_name); >> > > + >> > >> > The semantics of this being conditionally freed is a bit annoying, as >> > it is already replicated in 3 places. I suppose a helper would come in >> > hand. >> >> Yeh. >> >> I have already used ovl_cache_entry_free() in my tree. >> >> Thanks, >> Amir. >> >> > >> > In this specific case, it could just be: >> > >> > if (ret !=3D 1) >> > kfree(cf_name); >> > >> > >> > > + return ret >=3D 0; >> > > } >> > > >> > > static int ovl_check_whiteouts(const struct path *path, struct ovl_= readdir_data *rdd) >> > > @@ -357,12 +424,18 @@ static int ovl_dir_read_merged(struct dentry *= dentry, struct list_head *list, >> > > .list =3D list, >> > > .root =3D root, >> > > .is_lowest =3D false, >> > > + .map =3D NULL, >> > > }; >> > > int idx, next; >> > > const struct ovl_layer *layer; >> > > + struct ovl_fs *ofs =3D OVL_FS(dentry->d_sb); >> > > >> > > for (idx =3D 0; idx !=3D -1; idx =3D next) { >> > > next =3D ovl_path_next(idx, dentry, &realpath, &layer); >> > > + >> > > + if (ofs->casefold) >> > > + rdd.map =3D sb_encoding(realpath.dentry->d_sb); >> > > + >> > > rdd.is_upper =3D ovl_dentry_upper(dentry) =3D=3D realp= ath.dentry; >> > > rdd.in_xwhiteouts_dir =3D layer->has_xwhiteouts && >> > > ovl_dentry_has_xwhiteouts(dent= ry); >> > > @@ -555,7 +628,7 @@ static bool ovl_fill_plain(struct dir_context *c= tx, const char *name, >> > > container_of(ctx, struct ovl_readdir_data, ctx); >> > > >> > > rdd->count++; >> > > - p =3D ovl_cache_entry_new(rdd, name, namelen, ino, d_type); >> > > + p =3D ovl_cache_entry_new(rdd, name, namelen, NULL, 0, ino, d_= type); >> > > if (p =3D=3D NULL) { >> > > rdd->err =3D -ENOMEM; >> > > return false; >> > > @@ -1023,6 +1096,8 @@ int ovl_check_empty_dir(struct dentry *dentry,= struct list_head *list) >> > > >> > > del_entry: >> > > list_del(&p->l_node); >> > > + if (p->c_name !=3D p->name) >> > > + kfree(p->c_name); >> > > kfree(p); >> > > } >> > >> > -- >> > Gabriel Krisman Bertazi --=20 Gabriel Krisman Bertazi