[Libguestfs] [PATCH] file: Better support for read-only files

[Eric Blake]

On 3/2/21 1:12 PM, Richard W.M. Jones wrote:

>>>
>>>    h->fd = openat (dfd, file, flags);
>>> +  if (h->fd == -1 && !readonly) {
>>> +    int saved_errno = errno;
>>> +    flags = (flags & ~O_ACCMODE) | O_RDONLY;
>>> +    h->fd = openat (dfd, file, flags);
>>> +    if (h->fd == -1)
>>> +      errno = saved_errno;
>>> +    else
>>> +      h->can_write = false;
>>> +  }
>>>    if (h->fd == -1) {
>>>      nbdkit_error ("open: %s: %m", file);
>>
>> This will always report the error that failed open when using O_RDWR.
>> But if open(O_RDWR) fail with EPERM, and open(O_RDONLY) fails
>> with another error, the other error will be hidden.
>>
>> Maybe it is better to log the first error so we don't need to save errno
>> when trying to open in read only mode?
> 
> Maybe we could put it in a nbdkit_debug message?

Sure, I can do that as a followup.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org