On Thu, Jun 5, 2025 at 9:34 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, 5 Jun 2025 at 07:51, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> >
> > - The above fix contains a cast to non-const, which is not actually
> > needed. So add the necessary helpers postfixed with _c that allow the
> > cast to be removed (touches vfs files but only in trivial ways)
>
I must have snoozed the review of this one :-/
> Grr.
>
> I despise those "trivial ways".
>
> In particular, I despise how this renames the backing_file_user_path()
> helper to something actively *worse*.
>
> The "_c()" makes no sense as a name. Yes, I realize that the "c"
> stands for "const", but it still makes absolutely zero sense, since
> everybody wants the const version.
>
> The only user of the non-const version is the *ointernal*
> implementation that is never exported to other modules, and that could
> have the special name.
>
> Although I suspect it doesn't even need it, it could just use the
> backing_file(f) macro directly and that should just be moved to
> internal.h, and then the 'const'ness would come from the argument as
> required.
>
> In fact, most of the _internal_ vfs users don't even want the
> non-const version, ie as far as I can tell the user in
> file_get_write_access() would be perfectly happy with the const
> version too.
>
> So you made the *normal* case have an odd name, and then kept the old
> sane name for the case nobody else really wants to see.
>
> If anything, the internal non-const version is the one that should be
> renamed (and *not* using some crazy "_nc()" postfix nasty crud). Not
> the one that gets exported and that everybody wants.
>
IMO, it would be nicer to use backing_file_set_user_path()
(patch attached).
> So I could fix up that last commit to not hate it, but honestly, I
> don't want that broken state in the kernel in the first place.
>
Would you consider pulling ovl-update-6.16^
and applying the attached patch [*]?
Thanks,
Amir.
[*] I did not include the removal of non-const casting to keep this
patch independent of the ovl PR.
Feel free to add it to my patch or I can send the patch post merge
or cleanup of casting post merge.
From bc79491bf671b8a1d6603e0367963341339f943f Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@xxxxxxxxx>
Date: Fri, 6 Jun 2025 07:46:02 +0200
Subject: [PATCH] fs: constify file ptr in backing_file_user_path()
Add internal helper backing_file_set_user_path() for the only
two cases that need to modify user path.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/backing-file.c | 4 ++--
fs/file_table.c | 13 ++++++++-----
fs/internal.h | 1 +
include/linux/fs.h | 2 +-
4 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/fs/backing-file.c b/fs/backing-file.c
index 763fbe9b72b2..8c7396bff121 100644
--- a/fs/backing-file.c
+++ b/fs/backing-file.c
@@ -41,7 +41,7 @@ struct file *backing_file_open(const struct path *user_path, int flags,
return f;
path_get(user_path);
- *backing_file_user_path(f) = *user_path;
+ backing_file_set_user_path(f, user_path);
error = vfs_open(real_path, f);
if (error) {
fput(f);
@@ -65,7 +65,7 @@ struct file *backing_tmpfile_open(const struct path *user_path, int flags,
return f;
path_get(user_path);
- *backing_file_user_path(f) = *user_path;
+ backing_file_set_user_path(f, user_path);
error = vfs_tmpfile(real_idmap, real_parentpath, f, mode);
if (error) {
fput(f);
diff --git a/fs/file_table.c b/fs/file_table.c
index c04ed94cdc4b..8ac2fbbd4f6d 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -52,17 +52,20 @@ struct backing_file {
};
};
-static inline struct backing_file *backing_file(struct file *f)
-{
- return container_of(f, struct backing_file, file);
-}
+#define backing_file(f) container_of(f, struct backing_file, file)
-struct path *backing_file_user_path(struct file *f)
+struct path *backing_file_user_path(const struct file *f)
{
return &backing_file(f)->user_path;
}
EXPORT_SYMBOL_GPL(backing_file_user_path);
+void backing_file_set_user_path(struct file *f, const struct path *path)
+{
+ backing_file(f)->user_path = *path;
+}
+EXPORT_SYMBOL_GPL(backing_file_set_user_path);
+
static inline void file_free(struct file *f)
{
security_file_free(f);
diff --git a/fs/internal.h b/fs/internal.h
index 213bf3226213..3860b022e57c 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -101,6 +101,7 @@ extern void chroot_fs_refs(const struct path *, const struct path *);
struct file *alloc_empty_file(int flags, const struct cred *cred);
struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
+void backing_file_set_user_path(struct file *f, const struct path *path);
static inline void file_put_write_access(struct file *file)
{
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a4fd649e2c3f..c745aee9c88a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2813,7 +2813,7 @@ struct file *dentry_open_nonotify(const struct path *path, int flags,
const struct cred *cred);
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
const struct cred *cred);
-struct path *backing_file_user_path(struct file *f);
+struct path *backing_file_user_path(const struct file *f);
/*
* When mmapping a file on a stackable filesystem (e.g., overlayfs), the file
--
2.34.1
