Re: [Qemu-devel] Bug in virtio-9p when fstatting an fd referring to a file that no longer exists

[Sassan Panahinejad <sassan@sassan.me.uk>]

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This thread seems relevant:
http://www.mail-archive.com/linux-fsdevel@vger.kernel.org/msg09159.html
Unless things have changed, it looks like the problem is in the client
kernel (although note that there isn't support in qemu, even if the client
did send an fid associated with an open file!).
Any thoughts on a workaround for this?


Thanks
Sassan

On 28 April 2011 17:13, Sassan Panahinejad <sassan@sassan.me.uk> wrote:

> It should be possible for guest applications to fstat a file for which they
> have a valid file descriptor, even if the file has been removed.
> Demonstrated by the code sample below (fstat reports no such file or
> directory).
> Strangely it seems that reading from a file in this state works fine (and
> when both are run, the server receives a different fid for each).
> On any other filesystem, the code runs correctly. On our 9p filesystem it
> fails.
> Many applications (including bash) depend on this working correctly.
> I will continue investigating, but any thoughts anyone has on the subject
> would be appreciated.
>
>
> Thanks
> Sassan
>
>
> #include <stdio.h>
> #include <unistd.h>
> #include <fcntl.h>
> #include <sys/types.h>
> #include <sys/stat.h>
>
>
> int main(void)
> {
>         int ret;
>         struct stat statbuf;
>         int fd = open("test.txt", O_RDWR | O_CREAT, 0666);
>         if (fd < 0) {
>                 printf("open failed: %m\n");
>                 return 1;
>         }
>         ret = write(fd, "test1\n", 6);
>         if (ret < 0) {
>                 printf("write1 failed: %m\n");
>                 return 1;
>         }
>         ret = unlink("test.txt");
>         if (ret < 0) {
>                 printf("unlink failed: %m\n");
>                 return 1;
>         }
>         ret = fstat(fd, &statbuf);
>         if (ret < 0) {
>                 printf("fstat failed: %m\n");
>                 return 1;
>         }
>         return 0;
> }
>

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