On Tuesday 07 June 2011 02:08 PM, Daniel wrote:
Thank you, Pavan. It clarifies most of my doubts.
Only I can't find the branch of 'if sync-mtab == 1'. And I thought it
was without "YES fork()". Could you explain more about that, please?
Oh, the variable mtab_pid is what indicates whether the sync-mtab option
is set or not. Trace back the caller of fuse_mnt_add_mount(). The call
stack looks like below;
fuse_bridge.c:init() -> gf_fuse_mount() -> fuse_mount_sys() ->
fuse_mnt_add_mount().
In gf_fuse_mount(), the last parameter is passed as :
sync_mtab ? &ctx->mtab_pid : NULL
So, if the "sync-mtab" option is set, mtab_pid will be non-NULL.
Otherwise it will be NULL.
Now you can relate back to the condition in fuse_mnt_add_mount().
If mtab_pid is NULL, the "NO" condition in the flow-chart I provided
comes into picture. Otherwise the code follows the YES condition.
Pavan
Thanks a lot.
Dan
On Tue, 2011-06-07 at 12:29 +0530, Pavan T C wrote:
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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