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. 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". 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. -- Sincerely yours, Mike.
