On Fri, 29 Apr 2022 21:19:51 +0800 Bin Meng <bmeng...@gmail.com> wrote:
> On Fri, Apr 29, 2022 at 9:08 PM Greg Kurz <gr...@kaod.org> wrote: > > > > On Fri, 29 Apr 2022 14:46:26 +0200 > > Christian Schoenebeck <qemu_...@crudebyte.com> wrote: > > > > > On Freitag, 29. April 2022 13:28:39 CEST Bin Meng wrote: > > > > On Fri, Apr 29, 2022 at 7:16 PM Christian Schoenebeck > > > > > > > > <qemu_...@crudebyte.com> wrote: > > > > > Linux and macOS only share some errno definitions with equal macro > > > > > name and value. In fact most mappings for errno are completely > > > > > different on the two systems. > > > > > > > > > > This patch converts some important errno values from macOS host to > > > > > corresponding Linux errno values before eventually sending such error > > > > > codes along with 'Rlerror' replies (if 9p2000.L is used that is). Not > > > > > having translated errnos before violated the 9p2000.L protocol spec, > > > > > > > > > > which says: > > > > > " > > > > > size[4] Rlerror tag[2] ecode[4] > > > > > > > > > > ... ecode is a numerical Linux errno. > > > > > " > > > > > > > > > > > > > > > https://github.com/chaos/diod/wiki/protocol#lerror----return-error-code > > > > > > > > > > This patch fixes a bunch of misbehaviours when running a Linux client > > > > > > > > > > on macOS host. For instance this patch fixes: > > > > > mount -t 9p -o posixacl ... > > > > > > > > > > on Linux guest if security_mode=mapped was used for 9p server, which > > > > > refused to mount successfully, because macOS returned ENOATTR==93 > > > > > when client tried to retrieve POSIX ACL xattrs, because errno 93 > > > > > is defined as EPROTONOSUPPORT==93 on Linux, so Linux client believed > > > > > that xattrs were not supported by filesystem on host in general. > > > > > > > > This issue looks exact the same issue we were trying to fix when > > > > supporting 9p on Windows host, > > > > > > > > What we did is like this: > > > > http://patchwork.ozlabs.org/project/qemu-devel/patch/20220425142705.2099270-> > > > > 10-bmeng...@gmail.com/ > > > > > > > > But we had some questions in mind (see the commit message of our > > > > patch, and below) > > > > > > > > > Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com> > > > > > Link: > > > > > https://lore.kernel.org/qemu-devel/20220421124835.3e664669@bahia/ > > > > > Reviewed-by: Greg Kurz <gr...@kaod.org> > > > > > --- > > > > > > > > > > hw/9pfs/9p-util.h | 30 ++++++++++++++++++++++++++++++ > > > > > hw/9pfs/9p.c | 2 ++ > > > > > 2 files changed, 32 insertions(+) > > > > > > > > > > diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h > > > > > index 2cc9a5dbfb..c3526144c9 100644 > > > > > --- a/hw/9pfs/9p-util.h > > > > > +++ b/hw/9pfs/9p-util.h > > > > > @@ -58,6 +58,36 @@ static inline uint64_t host_dev_to_dotl_dev(dev_t > > > > > dev) > > > > > > > > > > #endif > > > > > } > > > > > > > > > > +/* Translates errno from host -> Linux if needed */ > > > > > +static inline int errno_to_dotl(int err) { > > > > > +#if defined(CONFIG_LINUX) > > > > > + /* nothing to translate (Linux -> Linux) */ > > > > > +#elif defined(CONFIG_DARWIN) > > > > > + /* > > > > > + * translation mandatory for macOS hosts > > > > > + * > > > > > + * FIXME: Only most important errnos translated here yet, this > > > > > should > > > > > be + * extended to as many errnos being translated as possible in > > > > > future. + */ > > > > > + if (err == ENAMETOOLONG) { > > > > > + err = 36; /* ==ENAMETOOLONG on Linux */ > > > > > + } else if (err == ENOTEMPTY) { > > > > > + err = 39; /* ==ENOTEMPTY on Linux */ > > > > > + } else if (err == ELOOP) { > > > > > + err = 40; /* ==ELOOP on Linux */ > > > > > + } else if (err == ENOATTR) { > > > > > + err = 61; /* ==ENODATA on Linux */ > > > > > + } else if (err == ENOTSUP) { > > > > > + err = 95; /* ==EOPNOTSUPP on Linux */ > > > > > + } else if (err == EOPNOTSUPP) { > > > > > + err = 95; /* ==EOPNOTSUPP on Linux */ > > > > > + } > > > > > > > > What happens if a macOS guest is running on QEMU from a macOS host? > > > > Here all macOS errnos are translated to the Linux errnos. Will macOS > > > > be happy? > > > > > > Look at the commit log of this patch: it is a matter of which protocol is > > > used > > > (currently there are 3 [1] protocol versions): > > > > > > * 9p2000: nothing to translate here, as this protocol version does not > > > return a numeric error code, it only returns an error string (and we > > > are > > > no longer supporting 9p2000 version in QEMU anyway BTW [1]): > > > http://ericvh.github.io/9p-rfc/rfc9p2000.html#anchor27 > > > > > > * 9p2000.L: errno *must* be in Linux errno mapping: > > > > > > https://github.com/chaos/diod/wiki/protocol#lerror----return-error-code > > > > > > * 9p2000.u: this one returns both an error code and error string, and > > > it > > > says the error string should be preferred being interpreted by > > > client: > > > http://ericvh.github.io/9p-rfc/rfc9p2000.u.html#anchor15 > > > > > > In this patch here I only translated errno for 9p2000.L, whereas you are > > > always translating it, no matter wich protocol version is used. You might > > > argue that there should be a translation for 9p2000.u as well, but in the > > > end > > > we don't know the OS running on guest in this case. It could be Linux or > > > something else. > > > > > > > In the case of 9p2000.u the spec says "to provide a hint of the underlying > > UNIX error number which caused the error on the server" and even mentions > > "consistency problems of mapping error numbers betweeen different versions > > of UNIX"... this basically means that errno in 9p2000.u is undefined since > > it depends on the host. It is thus unusable unless the guest runs a > > compatible > > UNIX variant. In any case, there's really nothing to translate. > > > > > [1] https://wiki.qemu.org/Documentation/9p#9p_Protocol > > > > > Thanks for the clarifications and pointers to different protocols! It > looks what we did in our Windows patch is correct. > > I have another question, does this mean the current 9pfs client on > macOS is broken since it does not use any translation? With this > patch, now the 9p server returns the translated linux errno so the 9p > client on macOS should complain. > I don't now the macOS client but if it doesn't expect linux errnos then it is infringing 9p2000.L and should be fixed. > Regards, > Bin