On Friday 01 February 2008 00:50, Tang, Changqing wrote:
> Jack:
> In order to open a new XRC domain, all processes on a node open a
> file descriptor using the
> same pathname, and pass the fd to ibv_open_xrc_domain().
>
> When can I close the fd ? when can I remove the temp file ? Can I
> close the fd and unlink the
> temp file right after ibv_open_xrc_domain() returns ?
>
> Does ibv_open_xrc_domain() increase the fd reference count and
> ibv_close_xrc_domain() decrease the
> fd reference count ?
>
I don't know what you mean by "unlink the temp file".
However, the following is true:
1. The first time ibv_open_xrc_domain() is used with a temp file, in kernel
space the temp file
descriptor is used to access the file's inode entry.
a. An xrc_domain "object" is created in kernel space, with a reference count
of 1.
b. A reference on the inode is taken (just once, at xrc_domain object
creation time,
for all ibv_open_xrc_domain() calls which arrive at that same inode).
c. Once you have an xrc_domain handle, you may close the temp file -- you've
already
got the xrc handle you need, and no longer need to go through the inode.
d. All subsequent calls to ibv_open_xrc_domain() for that inode will not
increment the
inode's reference count. However, each such call WILL increment the
xrc_domain object's
reference count. (a 2-layer reference counting system) -- and each such
call must
have a corresponding ibv_close_xrc_domain() call to decrement the
xrc_domain object's ref count.
2. ibv_close_xrc_domain()
a. decrements the xrc_domain object's ref count. If that count is then
zero, the inode
reference count is also decremented (see step 1.b above), and the
xrc_domain object
is destroyed.
Note: NO extra reference counts are taken on the fd -- only a single extra ref
count is taken
on the inode itself. (Thus, even if the file is removed, the inode
associated with the
file will still be kept, until all xrc_domain users have closed the xrc
domain).
Note 2: Even if you "remove" the file and create a new file with the same
filename before ALL
users of the previous domain have released (i.e., closed) the xrc
domain, the new file
will get a different inode entry, so there should be no xrc domain
collisions.
- Jack
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