Date: Sun, 11 Aug 2019 11:00:41 -0600 From: Ian Lepore <ian@freebsd.org> To: Alan Somers <asomers@freebsd.org> Cc: gljennjohn@gmail.com, Rick Macklem <rmacklem@uoguelph.ca>, "freebsd-current@FreeBSD.org" <freebsd-current@freebsd.org> Subject: Re: RFC: should lseek(SEEK_DATA/SEEK_HOLE) return ENOTTY? Message-ID: <c4472ee6c3f0602c616be594158c5f658129a24a.camel@freebsd.org> In-Reply-To: <CAOtMX2g=6cQdBpD2c7wS1ZaVFz08TDz-uauvCh_sS3VynLkR0g@mail.gmail.com> References: <YTBPR01MB3616B6F068199B6A3329432CDDD00@YTBPR01MB3616.CANPRD01.PROD.OUTLOOK.COM> <20190811090405.50cc49b1@ernst.home> <fe075daa384006c2056bb844cbccb6454c56fc3b.camel@freebsd.org> <CAOtMX2g=6cQdBpD2c7wS1ZaVFz08TDz-uauvCh_sS3VynLkR0g@mail.gmail.com>
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On Sun, 2019-08-11 at 09:12 -0600, Alan Somers wrote: > On Sun, Aug 11, 2019 at 8:57 AM Ian Lepore <ian@freebsd.org> wrote: > > > > On Sun, 2019-08-11 at 09:04 +0200, Gary Jennejohn wrote: > > > On Sun, 11 Aug 2019 02:03:10 +0000 > > > Rick Macklem <rmacklem@uoguelph.ca> wrote: > > > > > > > Hi, > > > > > > > > I've noticed that, if you do a lseek(SEEK_DATA/SEEK_HOLE) on a > > > > file > > > > that > > > > resides in a file system that does not support holes, ENOTTY is > > > > returned. > > > > > > > > This error isn't listed for lseek() and seems a liitle weird. > > > > > > > > > > ENOTTY is the standard error return for an unimplemented > > > ioctl(2), > > > and SEEK_HOLE ultimately becomes a call to fo_ioctl(). > > > > > > > I can see a couple of alternatives to this: > > > > 1 - Return a different error. Maybe ENXIO? > > > > or > > > > 2 - Have lseek() do the trivial implementation when the > > > > VOP_IOCTL() > > > > fails. > > > > - For SEEK_DATA, just return the offset given as argument > > > > and > > > > for SEEK_HOLE > > > > return the file's size as the offset. > > > > > > > > What do others think? rick > > > > ps: The man page should be updated, whatever is done w.r.t. > > > > this. > > > > > > > > > > I also vote for option 2 > > > > > > > If SEEK_DATA and SEEK_HOLE don't return the standard "ioctl not > > supported" error code and return a fake result, how are you > > supposed to > > determine at runtime whether SEEK_HOLE is supported or not? > > > > -- Ian > > pathconf(2) will tell you. > Ahh, I wasn't aware of that. For option 2, lseek() has to not just return the info, but must also actually set the file position accordingly, and has to treat offset >= filesize as an error. -- Ian
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