[Virtio-fs] [PATCH 0/9] virtiofsd: Allow using file handles instead of O_PATH FDs
Max Reitz
mreitz at redhat.com
Fri Jun 4 16:13:28 UTC 2021
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(-)
--
2.31.1
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