[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [MirageOS-devel] Mirage-Block-Unix Error
Okay, so I ran it with strace and the offending line is:
write(4, "\377\377\377\377\377\377\377\377\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576) = -1 EINVAL (Invalid argument)
I then looked up EINVAL errors and found the following description of cases when EINVAL is returned: fd is attached to an object which is unsuitable for writing; or the file was opened with the O_DIRECT flag, and either the address specified
in buf, the value specified in count, or the current file offset is not suitably aligned.
Then I looked at where the file was opened and found that the O_DIRECT flag is used: open("disk12.img", O_RDWR|O_DIRECT) = 4 So I looked up O_DIRECT and found this: The O_DIRECT flag on its own makes an effort
to transfer data synchronously, but does not give the
guarantees of the O_SYNC flag that data and necessary metadata
are transferred. To guarantee synchronous I/O, O_SYNC must be
used in addition to O_DIRECT. So I modified mirage-block-unix to add O_SYNC in odirect_stubs.c, because I thought that might help, but no such luck. Luckily I then noticed that prepending "buffered:" to the filename forces buffered IO, and that actually fixed my problem. I'm not sure what the exact reason for the failure is, but I thought the insight that I gained was interesting and might lead to someone fixing it. For now I will just use the workaround though! Rupert
On 5 March 2016 at 08:25, Rupert Horlick <rh572@xxxxxxxxx> wrote:
> Hi all,
>
> I'm running into a very strange issue using mirage-block-unix and I was
> wondering if anyone had some insight.
>
> The core of the issue is that connecting to the same file (disk.img or
> whatever) and writing in two different locations is giving completely
> different results.
>
> If I connect and write to offset 0 in my unix home directory (an NFS
> directory), then everything is completely fine. If I then go to
> /local/scratch (local scratch space on a department machine, so it's on the
> directly attached disk), and connect and write in exactly the same way I get
> the following error:
>
> (Failure "write: Invalid argument in write '' at file disk.img offset 0 with
> length 512")
>
> I've done the same thing in various other locations and never run into this
> error before. I've triple checked permissions and everything should be
> completely fine. Any ideas?
Try running it with "strace". That should show you the actual error
from the kernel.
--
Dr Thomas Leonard http://roscidus.com/blog/
GPG: DA98 25AE CAD0 8975 7CDA BD8E 0713 3F96 CA74 D8BA
_______________________________________________
MirageOS-devel mailing list
MirageOS-devel@xxxxxxxxxxxxxxxxxxxx
http://lists.xenproject.org/cgi-bin/mailman/listinfo/mirageos-devel
|
