Date: Sat, 26 Sep 2020 23:33:45 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: FreeBSD Hackers <freebsd-hackers@freebsd.org>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org> Subject: RFC: should copy_file_range(2) remain Linux compatible or support special files? Message-ID: <YTBPR01MB3966966F82008C9E471708FCDD370@YTBPR01MB3966.CANPRD01.PROD.OUTLOOK.COM>
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I know cross-posting is frowned upon, but I wanted everyone who might like to comment to see this. Currently copy_file_range(2) only supports regular files, which is compatible with the Linux one, where EINVAL is returned when either file descriptor refers to a non-regular file. Alan Somers would like to extend the syscall to handle special files. I think he has a couple of reasons for this (he can correct me): - When integrating it into "cp", he needed to provide a fallback for special files and similar fallbacks would probably be needed for other utilities like "dd". - iSCSI provides a "copy" operation which could be implemented using copy_file_range(2)/VOP_COPY_FILE_RANGE() if it supported special files. kib@ was concerned that a copy from /dev/zero would fill a disk, but I think that issue can be dealt with by limiting the duration of the syscall to 1sec (so that the utility can be terminated via SIGTERM or similar). I am on the fence w.r.t. since I modelled it after the Linux one and keeping it Linux compatible would facilitate portable code, but I understand why Alan Somers wants to extend it (the iSCSI support seems particularily useful). Everyone, please comment on this, rick
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