Benjamin LaHaise a écrit :
> On Tue, Sep 13, 2005 at 09:04:32AM +0200, Eric Dumazet wrote:
> 
>>I wish a process param could allow open() to take any free fd available, 
>>not the lowest one. One can always use fcntl(fd, F_DUPFD, slot) to move a 
>>fd on a specific high slot and always keep the 64 first fd slots free to 
>>speedup the kernel part at open()/dup()/socket() time.
> 
> 
> The overhead is easy to avoid by making use of dup2() and close() to keep 
> the lowest file descriptors in the table free, allowing open() and socket() 
> to always return 3 or 4.

Yes, this is what I described :) Maybe this was not clear.

> 
> Alternatively, the kernel could track available file descriptors using a 
> tree to efficiently insert freed slots into an ordered list of free 
> regions (something similar to the avl tree used in vmas).  Is it worth 
> doing?

Well no, since a user app can manage itself this part if it happens to be 
performance critical.


Sample of a user land lib : Each time a new fd is returned by 
open()/socket()/pipe()/accept()... the thread should call

fd = fdcache_dupfd(fd);

And close the file using  fdcache_closefd(fd) instead of close(fd);

Eric