From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Chen, Tiejun" <tiejun.chen@intel.com>
Subject: Re: [v6][PATCH 2/7] tools/libxc: introduce hypercall
	for xc_reserved_device_memory_map
Date: Fri, 12 Sep 2014 10:43:37 +0800
Message-ID: <54125DD9.2010805@intel.com>
References: <1410328190-6372-1-git-send-email-tiejun.chen@intel.com>
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To: Jan Beulich <JBeulich@suse.com>
Cc: kevin.tian@intel.com, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org, yang.z.zhang@intel.com
List-Id: xen-devel@lists.xenproject.org

On 2014/9/11 23:21, Jan Beulich wrote:
>>>> On 10.09.14 at 07:49, <tiejun.chen@intel.com> 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