Re: [Xen-devel] [v6][PATCH 2/7] tools/libxc: introduce hypercall for xc_reserved_device_memory_map

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/9/11 23:21, Jan Beulich wrote:
> > > > On 10.09.14 at 07:49, <tiejun.chen@xxxxxxxxx> wrote:
> > +    if ( errno == ENOBUFS )
> > +        *max_entries = memmap.nr_entries;
> > +
> > +    return rc ? -errno : memmap.nr_entries;
> > +}
> Isn't libxc generally aiming at using POSIX style return values, i.e. -1
> one error with errno indicating the details? Furthermore you're even
> inconsistent with yourself, as you return -1 in an earlier error path.
tools/libxc/xc_domain.c:

int xc_get_machine_memory_map(xc_interface *xch,
                              struct e820entry entries[],
                              uint32_t max_entries)
{
    int rc;
    struct xen_memory_map memmap = {
        .nr_entries = max_entries
    };
    DECLARE_HYPERCALL_BOUNCE(entries, sizeof(struct e820entry) * 
max_entries,
                             XC_HYPERCALL_BUFFER_BOUNCE_OUT);

    if ( !entries || xc_hypercall_bounce_pre(xch, entries) || 
max_entries <= 1)
        return -1;


    set_xen_guest_handle(memmap.buffer, entries);

    rc = do_memory_op(xch, XENMEM_machine_memory_map, &memmap, 
sizeof(memmap));
    xc_hypercall_bounce_post(xch, entries);

    return rc ? rc : memmap.nr_entries;
}

Here I just change last line as follows:

return rc ? -errno : memmap.nr_entries;

Because if I don't return '-errno', how will the caller know the 
detailed error?
    rc = xc_reserved_device_memory_map(xch, xmrdm, &nr_entries);
    if ( rc < 0 )
    {
        /* DRM doesn't exist. */
        if ( rc == -ENOENT )
            rc = 0;

Or are you saying we should use errno ditectly,

+
+        rc = xc_reserved_device_memory_map(xch, xmrdm, &nr_entries);
+        if (rc < 0 ) {
+            switch (errno) {
+            case ENOENT: /* RDM doesn't exist. */


Right?

Thanks
Tiejun

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