Re: filedesc(9) rewrite, please review

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Mon, 15 Oct 2018 16:05:34 +0000
    From:        coypu%sdf.org@localhost
    Message-ID:  <20181015160534.GA15839%SDF.ORG@localhost>

  | attached is the generated output of a filedesc(9) rewrite.

Did I miss something sometime, is there a real need for this?


  | FUNCTIONS
  |      The following functions are high-level interface routines to access the
  |      file descriptor table for a process and its file entries.
  |
  |      fd_alloc(p, want, *result)
  | 	      Create a new open file entry and allocate a file descriptor for
  | 	      the process p.  This operation is performed by invoking
  | 	      fd_alloc() to allocate the new file descriptor.

fd_alloc() uses fd_alloc() ?

In the existing version, falloc() used fdalloc() - have two functions been
merged into one?   If so, that sentence should be deleted.   Otherwise
something needs a new name.

  |                 The caller to
  | 	      the fd_alloc() function is responsible for expanding the file
  | 	      descriptor table when necessary.

That's ugly.  Why?   Cannot it be passed a pointer to the tabe,
and realloc for itself when needed?

  | 	      The index of the file entry is returned in *result.  The
  | 	      fd_alloc() function returns zero on success, otherwise an
  | 	      appropriate error is returned.

And what is "want" ?

  |      fd_alloc(p, want, *result)
  | 	      Allocate a file descriptor want for process p.  The resultant
  | 	      file descriptor is returned in *result.  The fd_alloc() function
  | 	      returns zero on success, otherwise an appropriate error is
  | 	      returned.

fd_alloc() again, same params, but now want is explained.

  |      fd_closeexec(void)
  | 	      Close any files for the current process that are marked close
  | 	      on exec.	This operation is performed by invoking fd_close() on
  | 	      the appropriate file descriptor.

descriptors

  |      fd_tryexpand(p)
  | 	      Expand the file descriptor table for process p by allocating
  | 	      memory for additional file descriptors.

Why "try" ?

  |      fd_free(void)
  | 	      Decrement the reference count on the file descriptor table for
  | 	      the current lwp and release the file descriptor table if the
  | 	      reference count drops to zero.


Impact upon any open files in the table ?

  |      fd_init(fdp)
  | 	      Create a file descriptor table using the same current and root
  | 	      directories of the current process.  The returned file
  | 	      descriptor table is guaranteed to have a reference count of one.

What is fdp?
And I think something needs to explain why directories are there.

kre