Date: Sat, 20 Apr 2019 11:44:34 -0700 From: Mark Millard <marklmi@yahoo.com> To: Igor Mozolevsky <igor@hybrid-lab.co.uk> Cc: Ian Lepore <ian@freebsd.org>, Hackers freeBSD <freebsd-hackers@freebsd.org> Subject: Re: bhyve VM stopped to boot after moving virtio disks Message-ID: <E8014037-6A9E-423A-B369-8C06AF024808@yahoo.com> In-Reply-To: <CADWvR2iR2THrrx7yK%2BguWKn_Zydnb%2BSFgD5FHFhVk-XeAzyZHQ@mail.gmail.com> References: <alpine.BSF.2.20.1904192255290.97274@puchar.net> <2006ff8da153bbe5e7f620da9260ee1518bd248f.camel@freebsd.org> <alpine.BSF.2.20.1904201729190.99712@puchar.net> <b0d23ad4b9f442a1a7342306443b855407f0765c.camel@freebsd.org> <CADWvR2iR2THrrx7yK%2BguWKn_Zydnb%2BSFgD5FHFhVk-XeAzyZHQ@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 2019-Apr-20, at 10:45, Igor Mozolevsky <igor at hybrid-lab.co.uk> = wrote: > On Sat, 20 Apr 2019 at 18:00, Ian Lepore wrote: >=20 > <snip> >> dd absolutely will fail to copy the last block of the source if it >> isn't exactly the blocksize and you didn't specify conv=3Dsync, and = it >> will return a zero status when doing so. It appears you've convinced >> yourself otherwise, but for anyone else reading this thread, be = aware: >> conv=3Dsync is required to copy the last part of the source if it's >> smaller than the blocksize. >=20 >=20 > Isn't that contrary to the POSIX Spec? Reading the manual [1], it is > implied (from STDERR part of the main section) that dd will read and > write partial blocks, cf. truncated blocks?.. >=20 > 1. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/dd.html Have you tried as Ian suggests to see if it made a difference? Ian seems to be speaking FreeBSD, not necessarily POSIX. (I'm talking actual FreeBSD behavior here, not necessarily documented behavior.) It turns out that https://www.freebsd.org/cgi/man.cgi?dd(1) does say: Normally, data resulting from input or conversion or both are = aggregated into output blocks of the specified size. After the end of input = is reached, any remaining output is written as a block. This means = that the final output block may be shorter than the output block size. where conv=3Dsync is described as: sync Pad every input block to the input buffer size. Spaces are used for pad bytes if a block oriented conversion value is specified, otherwise NUL bytes are used. (So sync changes the overall input size when it adds pad bytes, at least as documented.) It appears to me that Ian's expectations of the actual behavior and the FreeBSD documentation of such are not a match. Absent testing, I'd bet on Ian, even if it means FreeBSD dd has a bug. =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?E8014037-6A9E-423A-B369-8C06AF024808>