[0/9] virtiofsd: Allow using file handles instead of O_PATH FDs

Message

Max Reitz June 4, 2021, 4:13 p.m. UTC

Hi,

This is the C virtiofsd equivalent to
https://gitlab.com/virtio-fs/virtiofsd-rs/-/merge_requests/26.  As such,
the summary is pretty much the same:

Storing an O_PATH file descriptor in every lo_inode object means we have
a lot of FDs open, which is sometimes bad.  This series adds an option
(-o inode_file_handles) that will make virtiofsd attempt to generate a
file handle for new inodes and store that instead of an FD.  When an FD
is needed for a given inode, we open the handle.

To accomplish this, lo_inode.fd is should not be accessed directly
anymore, but only through helper functions (mainly lo_inode_fd() and
lo_inode_open()).  A TempFd object is added to hide the difference
between FDs that are bound to the lo_inode object (and so need not be
closed after use) and temporary FDs from open_by_handle_at() (which do
need to be closed after use).

To prevent the problem I spent a long time talking about (if we don’t
have an FD open for every inode, the inode can be deleted, its ID
reused, and then the lookup in lo_data.inodes will find the old deleted
inode), patch 7 adds a second hash table lo_data.inodes_by_handle that
maps file handles to lo_inode objects.  (Because file handles include a
generation ID, so we can discern between the old and the new inode.)

Patch 9 is completely optional, but I just really felt compelled to
write it.


Max Reitz (9):
  virtiofsd: Add TempFd structure
  virtiofsd: Use lo_inode_open() instead of openat()
  virtiofsd: Add lo_inode_fd() helper
  virtiofsd: Let lo_fd() return a TempFd
  virtiofsd: Let lo_inode_open() return a TempFd
  virtiofsd: Add lo_inode.fhandle
  virtiofsd: Add inodes_by_handle hash table
  virtiofsd: Optionally fill lo_inode.fhandle
  virtiofsd: Add lazy lo_do_find()

 tools/virtiofsd/helper.c              |   3 +
 tools/virtiofsd/passthrough_ll.c      | 809 +++++++++++++++++++++-----
 tools/virtiofsd/passthrough_seccomp.c |   2 +
 3 files changed, 667 insertions(+), 147 deletions(-)

Comments

Connor Kuehl June 4, 2021, 9:17 p.m. UTC | #1

On 6/4/21 11:13 AM, Max Reitz wrote:
> Hi,
> 
> This is the C virtiofsd equivalent to
> https://gitlab.com/virtio-fs/virtiofsd-rs/-/merge_requests/26.  As such,
> the summary is pretty much the same:
> 
> Storing an O_PATH file descriptor in every lo_inode object means we have
> a lot of FDs open, which is sometimes bad.  This series adds an option
> (-o inode_file_handles) that will make virtiofsd attempt to generate a
> file handle for new inodes and store that instead of an FD.  When an FD
> is needed for a given inode, we open the handle.
> 
> To accomplish this, lo_inode.fd is should not be accessed directly
> anymore, but only through helper functions (mainly lo_inode_fd() and
> lo_inode_open()).  A TempFd object is added to hide the difference
> between FDs that are bound to the lo_inode object (and so need not be
> closed after use) and temporary FDs from open_by_handle_at() (which do
> need to be closed after use).
> 
> To prevent the problem I spent a long time talking about (if we don’t
> have an FD open for every inode, the inode can be deleted, its ID
> reused, and then the lookup in lo_data.inodes will find the old deleted
> inode), patch 7 adds a second hash table lo_data.inodes_by_handle that
> maps file handles to lo_inode objects.  (Because file handles include a
> generation ID, so we can discern between the old and the new inode.)
> 
> Patch 9 is completely optional, but I just really felt compelled to
> write it.
> 
> 
> Max Reitz (9):
>   virtiofsd: Add TempFd structure
>   virtiofsd: Use lo_inode_open() instead of openat()
>   virtiofsd: Add lo_inode_fd() helper
>   virtiofsd: Let lo_fd() return a TempFd
>   virtiofsd: Let lo_inode_open() return a TempFd
>   virtiofsd: Add lo_inode.fhandle
>   virtiofsd: Add inodes_by_handle hash table
>   virtiofsd: Optionally fill lo_inode.fhandle
>   virtiofsd: Add lazy lo_do_find()
> 
>  tools/virtiofsd/helper.c              |   3 +
>  tools/virtiofsd/passthrough_ll.c      | 809 +++++++++++++++++++++-----
>  tools/virtiofsd/passthrough_seccomp.c |   2 +
>  3 files changed, 667 insertions(+), 147 deletions(-)
> 

For the series:

Reviewed-by: Connor Kuehl <[e-mail]>