Hi Joe,

On Mon, Oct 21, 2019 at 5:37 PM Joe Perches [off-list ref] wrote:

On Mon, 2019-10-21 at 16:37 +0200, Geert Uytterhoeven wrote:

quoted

The existing debugfs_create_ulong() function supports objects of
type "unsigned long", which are 32-bit or 64-bit depending on the
platform, in decimal form.  To format objects in hexadecimal, various
debugfs_create_x*() functions exist, but all of them take fixed-size
types.

Add a debugfs helper for "unsigned long" objects in hexadecimal format.
This avoids the need for users to open-code the same, or introduce
bugs when casting the value pointer to "u32 *" or "u64 *" to call
debugfs_create_x{32,64}().

[]

quoted

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h

[]

quoted

@@ -356,4 +356,14 @@ static inline ssize_t debugfs_write_file_bool(struct file *file,

 #endif

+static inline void debugfs_create_xul(const char *name, umode_t mode,
+                                   struct dentry *parent,
+                                   unsigned long *value)
+{
+     if (sizeof(*value) == sizeof(u32))
+             debugfs_create_x32(name, mode, parent, (u32 *)value);
+     else
+             debugfs_create_x64(name, mode, parent, (u64 *)value);

trivia: the casts are unnecessary.

They are necessary, in both calls (so using #ifdef as suggested below
won't help):

    include/linux/debugfs.h:375:42: error: passing argument 4 of
‘debugfs_create_x32’ from incompatible pointer type
[-Werror=incompatible-pointer-types]
       debugfs_create_x32(name, mode, parent, value);
                                              ^~~~~
    include/linux/debugfs.h:114:6: note: expected ‘u32 * {aka unsigned
int *}’ but argument is of type ‘long unsigned int *’
     void debugfs_create_x32(const char *name, umode_t mode, struct
dentry *parent,
          ^~~~~~~~~~~~~~~~~~
    include/linux/debugfs.h:377:42: error: passing argument 4 of
‘debugfs_create_x64’ from incompatible pointer type
[-Werror=incompatible-pointer-types]
       debugfs_create_x64(name, mode, parent, value);
                                              ^~~~~
    include/linux/debugfs.h:116:6: note: expected ‘u64 * {aka long
long unsigned int *}’ but argument is of type ‘long unsigned int *’
     void debugfs_create_x64(const char *name, umode_t mode, struct
dentry *parent,
          ^~~~~~~~~~~~~~~~~~

This might be more sensible using #ifdef

static inline void debugfs_create_xul(const char *name, umode_t mode,
                                      struct dentry *parent,
                                      unsigned long *value)
{
#if BITS_PER_LONG == 64
        debugfs_create_x64(name, mode, parent, value);
#else
        debugfs_create_x32(name, mode, parent, value);
#endif
}

... at the expense of the compiler checking only one branch.

Just like "if (IS_ENABLED(CONFIG_<foo>)" (when possible) is preferred
over "#ifdef CONFIG_<foo>" because of compile-coverage, I think using
"if" here is better than using "#if".

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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