[RFC PATCH 5/5] use next syscall data to predefine the file descriptor value

Nadia Derbey Nadia.Derbey at bull.net
Wed Jul 9 23:25:48 PDT 2008


Eric W. Biederman wrote:
> Nadia.Derbey at bull.net writes:
> 
> 
>>[PATCH 05/05]
>>
>>This patch uses the value written into the next_syscall_data proc file
>>as a target file descriptor for the next file to be opened.
>>
>>This makes it easy to restart a process with the same fds as the ones it was
>>using during the checkpoint phase, instead of 1. opening the file, 2. dup2'ing
>>the open file descriptor.
> 
> 
> As it happens the behavior of open is deterministic.  So if you open
> the files in the right order you should not need this.  dup2 is only needed
> if there is a gap in the fds used.
> 

This covers the case where you're checkpointing a process that has
1. opened, say 3 files (fds x, x+1, and x+2)
2. closed fd x+1
--> checkpoint occurs at that point.

During restart, you'll have to only recreate fds x and x+2.

But I'm realizing that this might be what you're calling a gap in the 
fds ;-)

Regards,
Nadia




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