Re: [PATCH v6 3/8] file-posix: introduce get_sysfs_str_val for device zoned model

[Sam Li]

Stefan Hajnoczi <stefanha@redhat.com> 于2022年8月8日周一 21:52写道：
>
> On Fri, Aug 05, 2022 at 03:57:46PM +0800, Sam Li wrote:
> > Use sysfs attribute files to get the string value of device
> > zoned model. Then get_sysfs_zoned_model can convert it to
> > BlockZoneModel type in QEMU.
> >
> > Signed-off-by: Sam Li <faithilikerun@gmail.com>
> > Reviewed-by: Hannes Reinecke <hare@suse.de>
> > ---
> >  block/file-posix.c               | 70 ++++++++++++++++++++++++++++++++
> >  include/block/block_int-common.h |  3 ++
> >  2 files changed, 73 insertions(+)
> >
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index a40eab64a2..4785203eea 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1264,6 +1264,68 @@ out:
> >  #endif
> >  }
> >
> > +/*
> > + * Convert the zoned attribute file in sysfs to internal value.
> > + */
> > +static int get_sysfs_str_val(int fd, struct stat *st,
> > +                              const char *attribute,
> > +                              char **val) {
>
> The fd argument is unused and can be dropped.
>
> > +#ifdef CONFIG_LINUX
> > +    char *buf = NULL;
> > +    g_autofree char *sysfspath = NULL;
> > +    int ret;
> > +    size_t len;
> > +
> > +    if (!S_ISBLK(st->st_mode)) {
> > +        return -ENOTSUP;
> > +    }
> > +
> > +    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
> > +                                major(st->st_rdev), minor(st->st_rdev),
> > +                                attribute);
> > +    ret = g_file_get_contents(sysfspath, &buf, &len, NULL);
> > +    if (ret == -1) {
> > +        ret = -errno;
>
> g_file_get_contents() does not set errno. You can either pass in a
> GError and report the message string by converting it into a QEMU Error
> object (grep for g_file_get_contents() to see example), or you can
> return a fixed error code like -ENOENT.
>
> > +        return ret;
> > +    }
> > +
> > +    /* The file is ended with '\n' */
> > +    if (buf[len - 1] == '\n') {
> > +        buf[len - 1] = '\0';
> > +    }
> > +
> > +    if (!strncpy(*val, buf, len)) {
> > +        ret = -errno;
> > +        return ret;
> > +    }
> > +    g_free(buf);
>
> buf is not necessary. val can be passed directly to g_file_get_contents().
>
> > +    return 0;
> > +#else
> > +    return -ENOTSUP;
> > +#endif
> > +}
>
> Now get_sysfs_long_val() can be written using get_sysfs_str_val():
>
>   static long get_sysfs_long_val(struct stat *st, const char *attribute)
>   {
>       g_autofree char *str = NULL;
>       const char *end;
>       long val;
>       int ret;
>
>       ret = get_sysfs_str_val(st, attribute, &str);
>       if (ret < 0) {
>           return ret;
>       }
>
>       ret = qemu_strtol(str, &end, 10, &val);
>       if (ret == 0 && end && *end == '\0') {
>           ret = val;
>       }
>       return ret;
>   }
>
> The get_sysfs_long_val() patch can be moved after the
> get_sysfs_str_val() patch.

Cool! Will change it.

> > +
> > +static int get_sysfs_zoned_model(int fd, struct stat *st,
> > +                                 BlockZoneModel *zoned) {
> > +    g_autofree char *val = NULL;
> > +    val = g_malloc(32);
> > +    get_sysfs_str_val(fd, st, "zoned", &val);
>
> Once get_sysfs_str_val() passes val through to g_get_file_contents() the
> caller will no longer have to g_malloc() val themselves.