[PATCH 1/2] fs: Add fd_install file operation

[Joel Fernandes]

On Mon, Aug 3, 2020 at 10:47 AM 'Kalesh Singh' via kernel-team
<kernel-team at android.com> wrote:
>
> Provides a per process hook for the acquisition of file descriptors,
> despite the method used to obtain the descriptor.
>

Hi,
So apart from all of the comments received, I think it is hard to
understand what the problem is, what the front-end looks like etc.
Your commit message is 1 line only.

I do remember some of the challenges discussed before, but it would
describe the problem in the commit message in detail and then discuss
why this solution is fit.  Please read submitting-patches.rst
especially "2) Describe your changes".

thanks,

 - Joel


> Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
> ---
>  Documentation/filesystems/vfs.rst | 5 +++++
>  fs/file.c                         | 3 +++
>  include/linux/fs.h                | 1 +
>  3 files changed, 9 insertions(+)
>
> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
> index ed17771c212b..95b30142c8d9 100644
> --- a/Documentation/filesystems/vfs.rst
> +++ b/Documentation/filesystems/vfs.rst
> @@ -1123,6 +1123,11 @@ otherwise noted.
>  ``fadvise``
>         possibly called by the fadvise64() system call.
>
> +``fd_install``
> +       called by the VFS when a file descriptor is installed in the
> +       process's file descriptor table, regardless how the file descriptor
> +       was acquired -- be it via the open syscall, received over IPC, etc.
> +
>  Note that the file operations are implemented by the specific
>  filesystem in which the inode resides.  When opening a device node
>  (character or block special) most filesystems will call special
> diff --git a/fs/file.c b/fs/file.c
> index abb8b7081d7a..f5db8622b851 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -616,6 +616,9 @@ void __fd_install(struct files_struct *files, unsigned int fd,
>  void fd_install(unsigned int fd, struct file *file)
>  {
>         __fd_install(current->files, fd, file);
> +
> +       if (file->f_op->fd_install)
> +               file->f_op->fd_install(fd, file);
>  }
>
>  EXPORT_SYMBOL(fd_install);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index f5abba86107d..b976fbe8c902 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1864,6 +1864,7 @@ struct file_operations {
>                                    struct file *file_out, loff_t pos_out,
>                                    loff_t len, unsigned int remap_flags);
>         int (*fadvise)(struct file *, loff_t, loff_t, int);
> +       void (*fd_install)(int, struct file *);
>  } __randomize_layout;
>
>  struct inode_operations {
> --
> 2.28.0.163.g6104cc2f0b6-goog
>
> --
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