On 04.12.20 10:10, Jan Beulich wrote:
> 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?

Already fixed locally.

> 
>> +    .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.

Oh, indeed.

This is a remnant of an earlier variant.

> 
> 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.

In the end they do. Creating a complete direntry just for obtaining its
size is overkill, especially as hypfs_read_dyndir_id_entry() is not
directly calculating the size, but copying the fixed and the variable
parts in two portions.

> 
>> +    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));

Fine with me.

> 
> 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.

The problem with the lock is that it is rather user specific. For
domains this will be split (rcu_read_lock(&domlist_read_lock) for
the /domain directory, and get_domain() for the per-domain level).

And memory allocation might need other data as well, so this won't
be the same structure for all cases. A two level dynamic directory
(e.g. domain/vcpu) might want to allocate the needed dyndata for
both levels already when entering /domain.

> 
> 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?

Oh, indeed. Need to check against UINT_MAX.

> 
>> +    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?

Already fixed.

> 
>> +    .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?

Basically it just takes an additional parameter for the function vector.
Maybe I should rename it to HYPFS_DIR_INIT_FUNC()?

> 
>> +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 ...

I think I'll change it.


Juergen