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Date: Tue, 4 Aug 2020 11:41:09 -0700
From: Andre McCurdy <armccurdy@...il.com>
To: musl@...ts.openwall.com
Cc: Érico Rolim <erico.erc@...il.com>
Subject: Re: [PATCH v2] extend gethostid beyond a stub
On Tue, Aug 4, 2020 at 6:33 AM Érico Rolim <ericonr@...root.org> wrote:
>
> From: Érico Rolim <erico.erc@...il.com>
>
> Implement part of the glibc behavior, where the 32-bit identifier stored
> in /etc/hostid, if the file exists, is returned. If this file doesn't
> contain at least 32 bits or can't be opened for some reason, return 0.
> ---
>
> > The glibc implementation appears to read and write directly into an
> > int32_t variable, without any endianness conversion. To be
> > interoperable with /etc/hostid files created by glibc shouldn't musl
> > skip the ntohl() and just return x ?
>
> I have changed it to directly read the file into a variable. Given that
> the return type is long, should I still use int32_t inside the function?
Yes. Consider what happens on a big-endian 64bit system.
For reference, the glibc code is basically:
long int
gethostid (void)
{
int32_t id;
int fd;
/* First try to get the ID from a former invocation of sethostid. */
fd = __open_nocancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
if (fd >= 0)
{
ssize_t n = __read_nocancel (fd, &id, sizeof (id));
__close_nocancel_nostatus (fd);
if (n == sizeof (id))
return id;
}
...
}
> src/misc/gethostid.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/src/misc/gethostid.c b/src/misc/gethostid.c
> index 25bb35db..2877842f 100644
> --- a/src/misc/gethostid.c
> +++ b/src/misc/gethostid.c
> @@ -1,6 +1,18 @@
> #include <unistd.h>
> +#include <stdio.h>
>
> long gethostid()
> {
> - return 0;
> + FILE *f;
> + long rv = 0;
> +
> + f = fopen("/etc/hostid", "reb");
> + if (f) {
> + if (fread(&rv, 4, 1, f) == 0) {
> + rv = 0;
> + }
> + fclose(f);
> + }
> +
> + return rv;
> }
> --
> 2.28.0
>
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