[Gluster-devel] Why to fork so many times?

[Pavan T C]

On Tuesday 07 June 2011 10:54 AM, Daniel wrote:
> Hello hackers:
>
> I am learning glusterfs and get one question when I reading
> contrib/fuse-lib/mount.c fuse_mnt_add_mount(). Why does it fork four
> times and the grand-grand-child exec("/bin/mount")? What is the benefit
> and the consideration?

As I see it, it forks thrice. Here is what I understand from the code:

+---------------------+
| fuse_mnt_add_mount()|<------------------------------+
| fork and wait for   |                               |
| child to return     |                               |
+-----+---------------+                               |
       |                                               |
       |                                               |
       X                                               |
      / \                                              |
     /if \                                             |
    /sync-\    NO    +---------------------------+     |
   X mtab  X-------->| Do async ops by returning |     |
    \ == 1/   fork() | from here so that parent  |     |
     \   /           | does not wait. But before |     |
      \ /            | doing that, create a dummy|     |
       X             | parent to wait for child  |     |
       | YES         | that does the /bin/mount  |     |
       |             +------------+--------------+     |
       | fork()                   |                    |
       V                          |                    |
+-----+----------+               | fork() -> Parent returns here.
| Child: execl   |               v
| /bin/mount with|         +---------------+
| -f option to   |         |dummy parent:  |
| only populate  |  fork() | fork and wait |
| mtab but don't |<--------+ for /bin/mount|
| actually mount |         | to return     |
| anything.      |         +---------------+
+----------------+

HTH,
Pavan

>
> Thank you
>
> Daniel
>
>
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