Re: [PATCH v2 15/17] xen/cpupool: add cpupool directories

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.12.2020 09:21, Juergen Gross wrote:
> @@ -1003,12 +1006,131 @@ static struct notifier_block cpu_nfb = {
>      .notifier_call = cpu_callback
>  };
>  
> +#ifdef CONFIG_HYPFS
> +static const struct hypfs_entry *cpupool_pooldir_enter(
> +    const struct hypfs_entry *entry);
> +
> +static struct hypfs_funcs cpupool_pooldir_funcs = {

Yet one more const missing?

> +    .enter = cpupool_pooldir_enter,
> +    .exit = hypfs_node_exit,
> +    .read = hypfs_read_dir,
> +    .write = hypfs_write_deny,
> +    .getsize = hypfs_getsize,
> +    .findentry = hypfs_dir_findentry,
> +};
> +
> +static HYPFS_VARDIR_INIT(cpupool_pooldir, "%u", &cpupool_pooldir_funcs);
> +
> +static const struct hypfs_entry *cpupool_pooldir_enter(
> +    const struct hypfs_entry *entry)
> +{
> +    return &cpupool_pooldir.e;
> +}
> +
> +static int cpupool_dir_read(const struct hypfs_entry *entry,
> +                            XEN_GUEST_HANDLE_PARAM(void) uaddr)
> +{
> +    int ret = 0;
> +    const struct cpupool *c;
> +    unsigned int size = 0;
> +
> +    list_for_each_entry(c, &cpupool_list, list)
> +    {
> +        size += hypfs_dynid_entry_size(entry, c->cpupool_id);

Why do you maintain size here? I can't spot any use.

With this dropped the function then no longer depends on its
"entry" parameter, which makes me wonder ...

> +        ret = hypfs_read_dyndir_id_entry(&cpupool_pooldir, c->cpupool_id,
> +                                         list_is_last(&c->list, 
> &cpupool_list),
> +                                         &uaddr);
> +        if ( ret )
> +            break;
> +    }
> +
> +    return ret;
> +}
> +
> +static unsigned int cpupool_dir_getsize(const struct hypfs_entry *entry)
> +{
> +    const struct cpupool *c;
> +    unsigned int size = 0;
> +
> +    list_for_each_entry(c, &cpupool_list, list)
> +        size += hypfs_dynid_entry_size(entry, c->cpupool_id);

... why this one does. To be certain their results are consistent
with one another, I think both should produce their results from
the same data.

> +    return size;
> +}
> +
> +static const struct hypfs_entry *cpupool_dir_enter(
> +    const struct hypfs_entry *entry)
> +{
> +    struct hypfs_dyndir_id *data;
> +
> +    data = hypfs_alloc_dyndata(sizeof(*data));

I generally like the added type safety of the macro wrappers
around _xmalloc(). I wonder if it wouldn't be a good idea to have
such here as well, to avoid random mistakes like

    data = hypfs_alloc_dyndata(sizeof(data));

However I further notice that the struct allocated isn't cpupool
specific at all. It would seem to me that such an allocation
therefore doesn't belong here. Therefore I wonder whether ...

> +    if ( !data )
> +        return ERR_PTR(-ENOMEM);
> +    data->id = CPUPOOLID_NONE;
> +
> +    spin_lock(&cpupool_lock);

... these two properties (initial ID and lock) shouldn't e.g. be
communicated via the template, allowing the enter/exit hooks to
become generic for all ID templates.

Yet in turn I notice that the "id" field only ever gets set, both
in patch 14 and here. But yes, I've now spotted the consumers in
patch 16.

> +    return entry;
> +}
> +
> +static void cpupool_dir_exit(const struct hypfs_entry *entry)
> +{
> +    spin_unlock(&cpupool_lock);
> +
> +    hypfs_free_dyndata();
> +}
> +
> +static struct hypfs_entry *cpupool_dir_findentry(
> +    const struct hypfs_entry_dir *dir, const char *name, unsigned int 
> name_len)
> +{
> +    unsigned long id;
> +    const char *end;
> +    const struct cpupool *cpupool;
> +
> +    id = simple_strtoul(name, &end, 10);
> +    if ( end != name + name_len )
> +        return ERR_PTR(-ENOENT);
> +
> +    cpupool = __cpupool_find_by_id(id, true);

Silent truncation from unsigned long to unsigned int?

> +    if ( !cpupool )
> +        return ERR_PTR(-ENOENT);
> +
> +    return hypfs_gen_dyndir_entry_id(&cpupool_pooldir, id);
> +}
> +
> +static struct hypfs_funcs cpupool_dir_funcs = {

Yet another missing const?

> +    .enter = cpupool_dir_enter,
> +    .exit = cpupool_dir_exit,
> +    .read = cpupool_dir_read,
> +    .write = hypfs_write_deny,
> +    .getsize = cpupool_dir_getsize,
> +    .findentry = cpupool_dir_findentry,
> +};
> +
> +static HYPFS_VARDIR_INIT(cpupool_dir, "cpupool", &cpupool_dir_funcs);

Why VARDIR? This isn't a template, is it? Or does VARDIR really
serve multiple purposes?

> +static void cpupool_hypfs_init(void)
> +{
> +    hypfs_add_dir(&hypfs_root, &cpupool_dir, true);
> +    hypfs_add_dyndir(&cpupool_dir, &cpupool_pooldir);
> +}
> +#else
> +
> +static void cpupool_hypfs_init(void)
> +{
> +}
> +#endif

I think you want to be consistent with the use of blank lines next
to #if / #else / #endif. In cases when they enclose multiple entities,
I think it's generally better to have intervening blank lines
everywhere. I also think in such cases commenting #else and #endif is
helpful. But you're the maintainer of this code ...

Jan