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Message-ID: <CAOQ4uxhgz=ZZvfxXcECE-daWmwqOCEMWH5Nh_weOeDciP8xh9w@mail.gmail.com>
Date: Sat, 9 Aug 2025 17:13:29 +0200
From: Amir Goldstein <amir73il@...il.com>
To: André Almeida <andrealmeid@...lia.com>,
Miklos Szeredi <miklos@...redi.hu>
Cc: Theodore Tso <tytso@....edu>, Gabriel Krisman Bertazi <krisman@...nel.org>, linux-unionfs@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
kernel-dev@...lia.com
Subject: Re: [PATCH RFC v3 2/7] ovl: Create ovl_casefold() to support
casefolded strncmp()
On Fri, Aug 8, 2025 at 10:59 PM André Almeida <andrealmeid@...lia.com> wrote:
>
> To add overlayfs support casefold filesystems, create a new function
> ovl_casefold(), to be able to do case-insensitive strncmp().
>
> ovl_casefold() allocates a new buffer and stores the casefolded version
> of the string on it. If the allocation or the casefold operation fails,
> fallback to use the original string. The caller of the function is
> responsible of freeing the buffer.
>
> The other string to be compared is casefolded in a previous step and
> stored at `struct ovl_cache_entry` member `char *cf_name`.
>
> Finally, set the strncmp() parameters to the casefold versions of the
> names to achieve case-insensitive support.
>
> For the non-casefold names, nothing changes and the rb_tree
> search/insert functions just ignores this change.
>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
> Changes from v2:
> - Refactor the patch to do a single kmalloc() per rb_tree operation
> - Instead of casefolding the cache entry name everytime per strncmp(),
> casefold it once and reuse it for every strncmp().
> ---
> fs/overlayfs/readdir.c | 92 +++++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 80 insertions(+), 12 deletions(-)
>
> diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
> index 2f42fec97f76c2000f76e15c60975db567b2c6d6..422f991393dfae12bcacf326414b7ee19e486ac8 100644
> --- a/fs/overlayfs/readdir.c
> +++ b/fs/overlayfs/readdir.c
> @@ -71,20 +71,58 @@ static struct ovl_cache_entry *ovl_cache_entry_from_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, int len, char **dst)
> +{
> +#if IS_ENABLED(CONFIG_UNICODE)
> + const struct qstr qstr = { .name = str, .len = len };
> + int cf_len;
> +
> + if (!map || is_dot_dotdot(str, len))
if (!IS_ENABLED(CONFIG_UNICODE) || !map ||...
> + return -1;
Better return 0 for no casefolding.
> +
> + *dst = kmalloc(OVL_NAME_LEN, GFP_KERNEL);
> +
> + if (dst) {
> + cf_len = utf8_casefold(map, &qstr, *dst, OVL_NAME_LEN);
> +
> + if (cf_len > 0)
> + return cf_len;
need to kfree(*dst) in the error case
caller only responsible of free on success
> + }
> +#endif
> +
> + return -1;
Better return 0 for no casefolding.
> +}
> +
> static bool ovl_cache_entry_find_link(const char *name, int len,
> struct rb_node ***link,
> - struct rb_node **parent)
> + struct rb_node **parent,
> + struct unicode_map *map)
> {
> + int ret;
> + char *dst = NULL;
> bool found = false;
> + const char *str = name;
> struct rb_node **newp = *link;
>
> + ret = ovl_casefold(map, name, len, &dst);
> +
> + if (ret > 0) {
> + str = dst;
> + len = ret;
> + }
> +
> while (!found && *newp) {
> int cmp;
> + char *aux;
> struct ovl_cache_entry *tmp;
>
> *parent = *newp;
> +
> tmp = ovl_cache_entry_from_node(*newp);
> - cmp = strncmp(name, tmp->name, len);
> +
> + aux = tmp->cf_name ? tmp->cf_name : tmp->name;
> +
> + cmp = strncmp(str, aux, len);
> if (cmp > 0)
> newp = &tmp->node.rb_right;
> else if (cmp < 0 || len < tmp->len)
> @@ -94,27 +132,50 @@ static bool ovl_cache_entry_find_link(const char *name, int len,
> }
> *link = newp;
>
> + kfree(dst);
> +
> return found;
> }
>
> static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
> - const char *name, int len)
> + const char *name, int len,
> + struct unicode_map *map)
> {
> struct rb_node *node = root->rb_node;
> - int cmp;
> + struct ovl_cache_entry *p;
> + const char *str = name;
> + bool found = false;
> + char *dst = NULL;
> + int cmp, ret;
> +
> + ret = ovl_casefold(map, name, len, &dst);
> +
> + if (ret > 0) {
> + str = dst;
> + len = ret;
> + }
> +
> + while (!found && node) {
> + char *aux;
>
> - while (node) {
> - struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
> + p = ovl_cache_entry_from_node(node);
>
> - cmp = strncmp(name, p->name, len);
> + aux = p->cf_name ? p->cf_name : p->name;
> +
> + cmp = strncmp(str, aux, len);
> if (cmp > 0)
> node = p->node.rb_right;
> else if (cmp < 0 || len < p->len)
> node = p->node.rb_left;
> else
> - return p;
> + found = true;
> }
>
> + kfree(dst);
> +
> + if (found)
> + return p;
> +
> return NULL;
> }
>
> @@ -212,7 +273,7 @@ static bool ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
> struct rb_node *parent = NULL;
> struct ovl_cache_entry *p;
>
> - if (ovl_cache_entry_find_link(name, len, &newp, &parent))
> + if (ovl_cache_entry_find_link(name, len, &newp, &parent, rdd->map))
> return true;
>
> p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
> @@ -234,7 +295,7 @@ static bool ovl_fill_lowest(struct ovl_readdir_data *rdd,
> {
> struct ovl_cache_entry *p;
>
> - p = ovl_cache_entry_find(rdd->root, name, namelen);
> + p = ovl_cache_entry_find(rdd->root, name, namelen, rdd->map);
> if (p) {
> list_move_tail(&p->l_node, &rdd->middle);
> } else {
IMO, it is nicer to pass the cf_name to the low level rb tree lookup
helpers and call ovl_casefold() only in high level ovl_fill_merge().
This also deduplicates the code from patch 1 of storing the cf_name in
ovl_cache_entry_new().
something like this (untested) WDYT?
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index b65cdfce31ce..71efb29ad30f 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -79,10 +79,10 @@ static bool ovl_cache_entry_find_link(const char
*name, int len,
*parent = *newp;
tmp = ovl_cache_entry_from_node(*newp);
- cmp = strncmp(name, tmp->name, len);
+ cmp = strncmp(name, tmp->cf_name, len);
if (cmp > 0)
newp = &tmp->node.rb_right;
- else if (cmp < 0 || len < tmp->len)
+ else if (cmp < 0 || len < tmp->cf_len)
newp = &tmp->node.rb_left;
else
found = true;
@@ -101,10 +101,10 @@ static struct ovl_cache_entry
*ovl_cache_entry_find(struct rb_root *root,
while (node) {
struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
- cmp = strncmp(name, p->name, len);
+ cmp = strncmp(name, p->cf_name, len);
if (cmp > 0)
node = p->node.rb_right;
- else if (cmp < 0 || len < p->len)
+ else if (cmp < 0 || len < p->cf_len)
node = p->node.rb_left;
else
return p;
@@ -145,6 +145,7 @@ static bool ovl_calc_d_ino(struct ovl_readdir_data *rdd,
static struct ovl_cache_entry *ovl_cache_entry_new(struct
ovl_readdir_data *rdd,
const char *name, int len,
+ const char
*cf_name, int cf_len,
u64 ino, unsigned int d_type)
{
struct ovl_cache_entry *p;
@@ -156,6 +157,13 @@ static struct ovl_cache_entry
*ovl_cache_entry_new(struct ovl_readdir_data *rdd,
memcpy(p->name, name, len);
p->name[len] = '\0';
p->len = len;
+ if (cf_name && cf_name != name) {
+ p->cf_name == cf_name
+ p->cf_len = cf_len;
+ } else {
+ p->cf_name = p->name;
+ p->cf_len = len;
+ }
p->type = d_type;
p->real_ino = ino;
p->ino = ino;
@@ -175,17 +183,18 @@ static struct ovl_cache_entry
*ovl_cache_entry_new(struct ovl_readdir_data *rdd,
}
static bool ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
- const char *name, int len, u64 ino,
- unsigned int d_type)
+ const char *name, int len,
+ const char *cf_name, int cf_len,
+ u64 ino, unsigned int d_type)
{
struct rb_node **newp = &rdd->root->rb_node;
struct rb_node *parent = NULL;
struct ovl_cache_entry *p;
- if (ovl_cache_entry_find_link(name, len, &newp, &parent))
+ if (ovl_cache_entry_find_link(cf_name, cf_len, &newp, &parent))
return true;
- p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
+ p = ovl_cache_entry_new(rdd, name, len, cf_name, cf_len, ino, d_type);
if (p == NULL) {
rdd->err = -ENOMEM;
return false;
@@ -200,15 +209,17 @@ static bool ovl_cache_entry_add_rb(struct
ovl_readdir_data *rdd,
static bool ovl_fill_lowest(struct ovl_readdir_data *rdd,
const char *name, int namelen,
+ const char *cf_name, int cf_len,
loff_t offset, u64 ino, unsigned int d_type)
{
struct ovl_cache_entry *p;
- p = ovl_cache_entry_find(rdd->root, name, namelen);
+ p = ovl_cache_entry_find(rdd->root, cf_name, cf_len);
if (p) {
list_move_tail(&p->l_node, &rdd->middle);
} else {
- p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
+ p = ovl_cache_entry_new(rdd, name, namelen, cf_name, cf_len,
+ ino, d_type);
if (p == NULL)
rdd->err = -ENOMEM;
else
@@ -223,8 +234,11 @@ 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->cf_name != p->name)
+ kfree(p->cf_name);
kfree(p);
+ }
INIT_LIST_HEAD(list);
}
@@ -260,12 +274,26 @@ static bool ovl_fill_merge(struct dir_context
*ctx, const char *name,
{
struct ovl_readdir_data *rdd =
container_of(ctx, struct ovl_readdir_data, ctx);
+ char *cf_name;
+ int cf_len = 0;
+
+ if (ofs->casefold)
+ cf_len = ovl_casefold(rdd->map, name, namelen, &cf_name);
+
+ /* lookup in rb tree by casefolded name or orig name */
+ if (cf_len <= 0) {
+ cf_name = name;
+ cf_len = namelen;
+ }
rdd->count++;
- if (!rdd->is_lowest)
- return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
- else
- return ovl_fill_lowest(rdd, name, namelen, offset, ino, d_type);
+ if (!rdd->is_lowest) {
+ return ovl_cache_entry_add_rb(rdd, name, namelen,
cf_name, cf_len,
+ ino, d_type);
+ } else {
+ return ovl_fill_lowest(rdd, name, namelen, cf_name, cf_len,
+ offset, ino, d_type);
+ }
}
static int ovl_check_whiteouts(const struct path *path, struct
ovl_readdir_data *rdd)
@@ -555,7 +583,7 @@ static bool ovl_fill_plain(struct dir_context
*ctx, const char *name,
container_of(ctx, struct ovl_readdir_data, ctx);
rdd->count++;
- p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
+ p = ovl_cache_entry_new(rdd, name, namelen, NULL, 0, ino, d_type);
if (p == NULL) {
rdd->err = -ENOMEM;
return false;
> @@ -640,7 +701,8 @@ static int ovl_dir_read_impure(const struct path *path, struct list_head *list,
All the changes below this point related to code paths of
ovl_iterate_real(), ovl_dir_read_impure() and struct ovl_readdir_translate
are irrelevant to casefolding and not needed.
This code iterates a single layer "real directory" and "translates" real ino to
ovl ino in some cases, but it does not compare any names between layers.
Thanks,
Amir.
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