12:58 a.m.
Am 14.02.2021 um 10:20 schrieb Mike Rapoport
<rppt(a)kernel.org>:
On Fri, Feb 12, 2021 at 10:18:19AM +0100, David Hildenbrand wrote:
>> On 12.02.21 00:09, Mike Rapoport wrote:
>> On Thu, Feb 11, 2021 at 01:07:10PM +0100, David Hildenbrand wrote:
>>> On 11.02.21 12:27, Mike Rapoport wrote:
>>>> On Thu, Feb 11, 2021 at 10:01:32AM +0100, David Hildenbrand wrote:
>>>
>>> So let's talk about the main user-visible differences to other memfd
files
>>> (especially, other purely virtual files like hugetlbfs). With secretmem:
>>>
>>> - File content can only be read/written via memory mappings.
>>> - File content cannot be swapped out.
>>>
>>> I think there are still valid ways to modify file content using syscalls:
>>> e.g., fallocate(PUNCH_HOLE). Things like truncate also seems to work just
>>> fine.
>> These work perfectly with any file, so maybe we should have added
>> memfd_create as a flag to open(2) back then and now the secretmem file
>> descriptors?
>
> I think open() vs memfd_create() makes sense: for open, the path specifies
> main properties (tmpfs, hugetlbfs, filesystem). On memfd, there is no such
> path and the "type" has to be specified differently.
>
> Also, open() might open existing files - memfd always creates new files.
Yes, but still open() returns a handle to a file and memfd_create() returns
a handle to a file. The differences may be well hidden by e.g. O_MEMORY and
than features unique to memfd files will have their set of O_SOMETHING
flags.
Let‘s agree to disagree.
It's the same logic that says "we already have an interface
that's close
enough and it's fine to add a bunch of new flags there".
No, not quite. But let‘s agree to disagree.
And here we come to the question "what are the differences that justify a
new system call?" and the answer to this is very subjective. And as such we
can continue bikeshedding forever.
I think this fits into the existing memfd_create() syscall just fine, and I heard no
compelling argument why it shouldn‘t. That‘s all I can say.