On Wed, May 11, 2022 at 09:25:52AM +1000, Dave Chinner wrote:

quoted

I'd love something like:

ssize_t sz;
fsinfo_query query[] = {
    { .request = FSINFO_MOUNT_PATH },
    { .request = FSINFO_PROPAGATION },
    { .request = FSINFO_CHILDREN_IDS },
};

sz = fsinfo(dfd, "", AT_EMPTY_PATH,
                &query, ARRAY_SIZE(query),
                buf, sizeof(buf));

for (p = buf; p < buf + sz; ) {
{
    fsinfo_entry *e = (struct fsinfo_entry) p;
    char *data = p + sizeof(struct fsinfo_entry);

    switch(e->request) {
    case FSINFO_MOUNT_PATH:
        printf("mountpoint %s\n", data);
        break;
    case FSINFO_PROPAGATION:
        printf("propagation %x\n", (uintptr_t) data);
        break;
    case FSINFO_CHILDREN_IDS:
        fsinfo_child *x = (fsinfo_child *) data;
        for (i = 0; i < e->count; i++) {
            printf("child: %d\n", x[i].mnt_id);
        }
        break;
    ...
    }

    p += sizeof(struct fsinfo_entry) + e->len;
}

That's pretty much what a multi-xattr get operation looks like.
It's a bit more more intricate in the setup of the request/return
buffer, but otherwise the structure of the code is the same.

I just don't see why we need special purpose interfaces like this
for key/value information when small tweaks to the existing
generic key/value interfaces can provide exactly the same
functionality....

I don't say we need a new interface ;-) I'd be happy with whatever as
long as:

  * minimal strings parsing (wish than a requirement)
  * one syscall returns multiple key/value
  * can address mount table entries by ID
  * can ask for list of children (submounts)
  * extensible

if this will be possible with xattr (listxattr2(), or so) when great.

  Karel

-- 
 Karel Zak  [off-list ref]
 http://karelzak.blogspot.com