Re: [PATCH v3 2/4] util: Introduce read_file() and read_file_long() function

[Yumei Huang <yuhuang@redhat.com>]

On Wed, Oct 15, 2025 at 12:46 PM David Gibson
<david@gibson.dropbear.id.au> wrote:
>
> On Wed, Oct 15, 2025 at 11:50:53AM +0800, Yumei Huang wrote:
> > On Wed, Oct 15, 2025 at 7:28 AM David Gibson
> > <david@gibson.dropbear.id.au> wrote:
> > > On Tue, Oct 14, 2025 at 03:38:34PM +0800, Yumei Huang wrote:
> > > > Signed-off-by: Yumei Huang <yuhuang@redhat.com>
> [snip]
> > > > + * @path: Path to the sysctl file
> > > > + * @fallback: Default value if file can't be read
> > > > + *
> > > > + * Return: Parameter value, fallback on failure
> > > > +*/
> > > > +long read_file_long(const char *path, long fallback)
> > > > +{
> > > > +        char buf[32];
> > >
> > > Rather than just using a semi-arbitrary 32 here, I'd suggest defining
> > > a new constant similar to UINT16_STRLEN.  Except that's trickier for a
> > > type that doesn't have a known fixed width.  Pity the C library
> > > doesn't have constants for these AFAICT.
> >
> > I will just define a UINTMAX_STRLEN with (sizeof("2147483647")).
>
> That's not quite right.
>  - It should be INTMAX_STRLEN (signed), UINTMAX would be for the
>    unsigned version
>  - That assumes intmax_t is 32-bit which is probably not the case (it
>    will be 64-bit, maybe even 128-bit on modern systems)
>  - For signed cases, it's the minimum (negative) value that gives the
>    longest possible string (for 32-bit, "-2147483648")

Maybe we could take it as 64 bits for now? I'm not sure under which
circumstance we would read such a large number.

If you agree, the define could be:

   #define INTMAX_STRLEN (sizeof("-9223372036854775808"))

Or maybe define it to 20 directly :

   #define INTMAX_STRLEN 20

what do you think?
>
> --
> David Gibson (he or they)       | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au  | minimalist, thank you, not the other way
>                                 | around.
> http://www.ozlabs.org/~dgibson



-- 
Thanks,

Yumei Huang