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> Microsoft tried to bridge the Linux APIs to NT APIs in WSL1 just like WINE does for Windows APIs to Linux APIs WSL1 doesn’t implement the Linux syscall inter

> Microsoft tried to bridge the Linux APIs to NT APIs in WSL1 just like WINE does for Windows APIs to Linux APIs WSL1 doesn’t implement the Linux syscall interface on top of the user-mode Win32 or NT APIs. Rather, it runs in-kernel; it calls kernel-mode NT APIs (only some of which directly correspond to NT syscalls), and (I assume) also implements some aspects of the Linux APIs internally to itself. Its approach is rather different from that of Wine or Cygwin, both of which translate one user-space API to another; and also from the legacy Windows OS/2 and POSIX/Interix/SFU/SUA subsystems, which implement those APIs mostly in user space, on top of the NT user-space API. WSL1 is essentially unique; the closest analog is probably the Linux syscall emulation in FreeBSD/NetBSD, Solaris10/Illumos LX branded zones, and the old Linux iBCS2 personality - although those are all far easier because there is much less mapping in emulating the Linux API on another POSIX OS than one fundamentally non-POSIX. > But they ended up running into issues and limitations that made them change their approach. I don’t think those issues were inherently insurmountable, and solving them in the context of WSL1 would have made Windows a better platform, since many of those issues (e.g. poor filesystem performance) also impact native Win32 apps. But, they made a decision on where to invest their resources. WSL2’s implementation strategy requires less engineering work overall to reach a given outcome.

ziml77 4y ago
I specifically said NT APIs to differentiate from the Windows APIs. And my "just like WINE" comment was more to differentiate what they were doing with WSL1 from WSL2. My use of "just like" is too strong there. And I also don't think any of the problems were insurmountable. I'm still disappointed that they gave up on WSL1. (At least partially because I thought the whole Windows Subsystem concept was neat design)
- skissane 4y ago
  > I specifically said NT APIs to differentiate from the Windows APIs. It depends on what you mean by "NT APIs". If you mean the NT API exposed to user-mode (NT syscalls), no, that is insufficient to implement WSL1 (or anything else like it). If you mean to include kernel-mode-only NT APIs (including undocumented/private APIs which MS doesn't expose to third parties, even new APIs added specifically for WSL1 to consume), then yes that is. > the whole Windows Subsystem concept was neat design Also worth keeping in mind, that WSL1 is not an "environment subsystem" in the sense that Win32 is – or OS/2 and POSIX/etc were. It has a radically different architecture from a classic Windows NT environment subsystem.
  - ziml77 4y ago
    Ah my mistake about the subsystem implementation. My memory was fuzzy given the 5+ years since I read Windows Internals 7th Edition. Thanks for the correction!

ziml77 4y ago

I specifically said NT APIs to differentiate from the Windows APIs. And my "just like WINE" comment was more to differentiate what they were doing with WSL1 from WSL2. My use of "just like" is too strong there. And I also don't think any of the problems were insurmountable. I'm still disappointed that they gave up on WSL1. (At least partially because I thought the whole Windows Subsystem concept was neat design)

skissane 4y ago
> I specifically said NT APIs to differentiate from the Windows APIs. It depends on what you mean by "NT APIs". If you mean the NT API exposed to user-mode (NT syscalls), no, that is insufficient to implement WSL1 (or anything else like it). If you mean to include kernel-mode-only NT APIs (including undocumented/private APIs which MS doesn't expose to third parties, even new APIs added specifically for WSL1 to consume), then yes that is. > the whole Windows Subsystem concept was neat design Also worth keeping in mind, that WSL1 is not an "environment subsystem" in the sense that Win32 is – or OS/2 and POSIX/etc were. It has a radically different architecture from a classic Windows NT environment subsystem.
- ziml77 4y ago
  Ah my mistake about the subsystem implementation. My memory was fuzzy given the 5+ years since I read Windows Internals 7th Edition. Thanks for the correction!