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Message-ID: <CAOQ4uxjG9+Vwpn6n=j2-PrK8u5DMA_oVmnZvbSpstWAMVBOsPg@mail.gmail.com>
Date: Fri, 22 Aug 2025 18:53:21 +0200
From: Amir Goldstein <amir73il@...il.com>
To: André Almeida <andrealmeid@...lia.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, 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 v6 4/9] ovl: Create ovl_casefold() to support casefolded strncmp()
On Fri, Aug 22, 2025 at 4:17 PM André Almeida <andrealmeid@...lia.com> wrote:
>
> 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 version
> of the string on it. If the allocation or the casefold operation fails,
> 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 <amir73il@...il.com>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
> 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..dfc661b7bc3f87efbf14991e97cee169400d823b 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_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)
> +{
> + const struct qstr qstr = { .name = str, .len = len };
> + int cf_len;
> +
> + if (!IS_ENABLED(CONFIG_UNICODE) || !map || is_dot_dotdot(str, len))
> + return 0;
> +
> + *dst = kmalloc(NAME_MAX, GFP_KERNEL);
> +
> + if (dst) {
> + cf_len = utf8_casefold(map, &qstr, *dst, NAME_MAX);
> +
> + if (cf_len > 0)
> + return cf_len;
> + }
> +
> + kfree(*dst);
> + return 0;
> +}
> +
> 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 char *name, int len,
>
> *parent = *newp;
> tmp = ovl_cache_entry_from_node(*newp);
> - cmp = strncmp(name, tmp->name, len);
> + cmp = strncmp(name, tmp->c_name, len);
> if (cmp > 0)
> newp = &tmp->node.rb_right;
> - else if (cmp < 0 || len < tmp->len)
> + else if (cmp < 0 || len < tmp->c_len)
> newp = &tmp->node.rb_left;
> else
> found = 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 = ovl_cache_entry_from_node(node);
>
> - cmp = strncmp(name, p->name, len);
> + cmp = strncmp(name, p->c_name, len);
> if (cmp > 0)
> node = p->node.rb_right;
> - else if (cmp < 0 || len < p->len)
> + else if (cmp < 0 || len < p->c_len)
> node = p->node.rb_left;
> else
> return p;
> @@ -145,6 +169,7 @@ 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 *c_name, int c_len,
> u64 ino, unsigned int 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 = rdd->in_xwhiteouts_dir && d_type == DT_REG;
>
> + if (c_name && c_name != name) {
> + p->c_name = c_name;
> + p->c_len = c_len;
> + } else {
> + p->c_name = p->name;
> + p->c_len = len;
> + }
> +
> if (d_type == DT_CHR) {
> p->next_maybe_whiteout = rdd->first_maybe_whiteout;
> rdd->first_maybe_whiteout = 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 = &rdd->root->rb_node;
> struct rb_node *parent = 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 = ovl_cache_entry_new(rdd, name, len, ino, d_type);
> + p = ovl_cache_entry_new(rdd, name, len, c_name, c_len, ino, d_type);
> if (p == NULL) {
> rdd->err = -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 = ovl_cache_entry_find(rdd->root, name, namelen);
> + p = ovl_cache_entry_find(rdd->root, c_name, c_len);
> if (p) {
> list_move_tail(&p->l_node, &rdd->middle);
> + return 0;
> } else {
> - p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
> + p = ovl_cache_entry_new(rdd, name, namelen, c_name, c_len,
> + ino, d_type);
> if (p == NULL)
> rdd->err = -ENOMEM;
> else
> list_add_tail(&p->l_node, &rdd->middle);
> }
>
> - return rdd->err == 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 != 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 =
> container_of(ctx, struct ovl_readdir_data, ctx);
> + struct ovl_fs *ofs = OVL_FS(rdd->dentry->d_sb);
> + const char *c_name = NULL;
> + char *cf_name = NULL;
> + int c_len = 0, ret;
> +
> + if (ofs->casefold)
> + c_len = ovl_casefold(rdd->map, name, namelen, &cf_name);
> +
> + if (c_len <= 0) {
> + c_name = name;
> + c_len = namelen;
> + } else {
> + c_name = cf_name;
> + }
>
> rdd->count++;
> if (!rdd->is_lowest)
> - return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
> + ret = ovl_cache_entry_add_rb(rdd, name, namelen, c_name, c_len, ino, d_type);
> else
> - return ovl_fill_lowest(rdd, name, namelen, offset, ino, d_type);
> + ret = ovl_fill_lowest(rdd, name, namelen, c_name, c_len, offset, ino, d_type);
> +
> + /*
> + * If ret == 1, that means that c_name is being used as part of struct
> + * ovl_cache_entry and will be freed at ovl_cache_free(). Otherwise,
> + * c_name was found in the rb-tree so we can free it here.
> + */
> + if (ret != 1 && c_name != name)
> + kfree(c_name);
> +
> + return ret >= 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 = list,
> .root = root,
> .is_lowest = false,
> + .map = NULL,
> };
> int idx, next;
> const struct ovl_layer *layer;
> + struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
>
> for (idx = 0; idx != -1; idx = next) {
> next = ovl_path_next(idx, dentry, &realpath, &layer);
> +
> + if (ofs->casefold)
> + rdd.map = sb_encoding(realpath.dentry->d_sb);
> +
> rdd.is_upper = ovl_dentry_upper(dentry) == realpath.dentry;
> rdd.in_xwhiteouts_dir = layer->has_xwhiteouts &&
> ovl_dentry_has_xwhiteouts(dentry);
> @@ -555,7 +628,7 @@ 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;
> @@ -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 != p->name)
> + kfree(p->c_name);
> kfree(p);
OK I thought this was contained in ovl_cache_free().
If we need to repeat this check, we need a helper
ovl_cache_entry_free() to use instead of kfree(p)
everywhere even in ovl_dir_read_impure() when it won't
actually be needed.
I can make this change on commit no need to repost.
Thanks,
Amir.
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