Date: Sun, 20 Sep 2020 15:58:09 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Alan Somers <asomers@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: RFC: copy_file_range(3) Message-ID: <YTBPR01MB39666188FC89399B0D632FE8DD3D0@YTBPR01MB3966.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <CAOtMX2iFZZpoj%2Bap21rrju4hJoip6ZoyxEiCB8852NeH7DAN0Q@mail.gmail.com> References: <CAOtMX2iFZZpoj%2Bap21rrju4hJoip6ZoyxEiCB8852NeH7DAN0Q@mail.gmail.com>
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Alan Somers wrote: >copy_file_range(2) is nifty, but it has a few sharp edges: >1) Certain file systems don't support it, necessitating a write/read based >fallback >2) It doesn't handle sparse files as well as SEEK_HOLE/SEEK_DATA >3) It's slightly tricky to both efficiently deal with holes and also >promptly respond to signals > >These problems aren't terribly hard, but it seems to me like most >applications that use copy_file_range would share the exact same >solutions. In particular, I'm thinking about cp(1), dd(1), and >install(8). Those three could benefit from sharing a userland wrapper that >handles the above problems. > >Should we add such a wrapper to libc? If so, what should it be called, and >should it be public or just private to /usr/src ? There has been a discussion on src-committers which I suggested should be taken to a public mailing list. The basic question is... Whether or not the copy_file_range(2) syscall should be compatible with the Linux one. When I did the syscall, I tried to make it Linux-compatible, arguing that Linux is now a de-facto standard. The Linux syscall only works on regular files, which is why Alan's patch for cp required a "fallback to the old way" for VCHR files like /dev/null. He is considering a wrapper in libc to provide FreeBSD specific semantics, which I have no problem with, so long as the naming and man page make it clear that it is not compatible with the Linux syscall. (Personally, I'd prefer a wrapper in libc to making the actual syscall non-Linux compatible, but that is just mho.) Hopefully this helps clarify what Alan is asking, rick -Alan _______________________________________________ freebsd-hackers@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org"
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