Re: [Qemu-devel] [PATCH 00/13] 9p: reconcile virtfs with unlinked files

[Greg Kurz]

Aneesh,

Can you review this series please, and maybe provide feedback on the
patches for the linux client ?

Thanks.

--
Greg

On Mon, 27 Jun 2016 11:40:55 +0200
Greg Kurz <address@hidden> wrote:
> This series addresses a long standing issue in 9p, where most syscalls
> accessing file attributes out of file descriptor stop to work in the
> guest when the file gets unlinked:
> 
> open("./test.txt", O_RDWR|O_CREAT, 0666) = 4
> unlink("./test.txt")                    = 0
> fstat(4, 0x3fffc22108d0)                = -1 ENOENT (No such file or 
> directory)
> ftruncate(4, 0)                         = -1 ENOENT (No such file or 
> directory)
> utimensat(4, NULL, NULL, 0)             = -1 ENOENT (No such file or 
> directory)
> fgetxattr(4, "user.greg", NULL, 0)      = -1 ENOENT (No such file or 
> directory)
> flistxattr(4, NULL, 0)                  = -1 ENOENT (No such file or 
> directory)
> fchmod(4, 0)                            = -1 ENOENT (No such file or 
> directory)
> fchown(4, -1, -1)                       = -1 ENOENT (No such file or 
> directory)
> 
> There is also another case where ftruncate() unexpectedly fails:
> 
> open("./test.txt", O_RDWR|O_CREAT, 0666) = 4
> chmod("./test.txt", 0)                  = 0
> ftruncate(4, 0)                         = -1 EACCES (Permission denied)
> 
> Since the open+unlink sequence is widely used in applications, these
> failures are really a problem, and does not encourage people to using
> 9p mounts.
> 
> The root cause for all these errors is that QEMU uses path based syscalls to
> implement 9p operations on file attributes, even if the fid has an open fd.
> 
> This series adds new file ops to the internal fsdev API, following the example
> of already existing fstat, so that backends can access the fid file descriptor
> and pass it to ftruncate(), fchmod() and friends.
> 
> This can be tested with a linux guest, provided the 9p client in the kernel is
> fixed with the following patches, to ensure it passes open fids (fid 
> associated
> to a valid file descriptor) to the 9p server in QEMU.
> 
> https://sourceforge.net/p/v9fs/mailman/message/35175775/
> 
> With this series and the patched guest kernel, all the failures mentionned
> above no longer occur.
> 
> ---
> 
> Greg Kurz (13):
>       9p: synth: drop v9fs_ prefix
>       9p: factour out duplicate code from local_fstat() and local_lstat()
>       9p: introduce the v9fs_get_fd_fid() helper
>       9p: getattr: use fstat if we have a fd
>       9p: introduce ftruncate file op
>       oslib: support futimens() if available
>       9p: introduce futimens file op
>       9p: add a fd argument to xattr helpers
>       9p: introduce fchown file op
>       9p: introduce fchmod file op
>       9p: xattr fid to reference file fid
>       9p: introduce fgetxattr file op
>       9p: introduce flistxattr file op
> 
> 
>  fsdev/file-op-9p.h        |    9 ++
>  hw/9pfs/9p-handle.c       |   85 ++++++++++++---
>  hw/9pfs/9p-local.c        |  213 ++++++++++++++++++++++++++++----------
>  hw/9pfs/9p-posix-acl.c    |   80 ++++++++++----
>  hw/9pfs/9p-proxy.c        |   78 ++++++++++++--
>  hw/9pfs/9p-synth.c        |  249 
> +++++++++++++++++++++++++++------------------
>  hw/9pfs/9p-xattr-user.c   |   41 +++++--
>  hw/9pfs/9p-xattr.c        |   35 ++++--
>  hw/9pfs/9p-xattr.h        |   67 +++++++-----
>  hw/9pfs/9p.c              |  189 +++++++++++++++++++++++++++++-----
>  hw/9pfs/9p.h              |    3 +
>  hw/9pfs/cofs.c            |   79 ++++++++++++++
>  hw/9pfs/coth.h            |    7 +
>  hw/9pfs/coxattr.c         |   42 ++++++++
>  include/sysemu/os-posix.h |    1 
>  util/oslib-posix.c        |   10 ++
>  16 files changed, 896 insertions(+), 292 deletions(-)
> 
> --
> Greg
>