Re: [RFC] Payloads and transient filesystem support for user-cr

[Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org>]

On 03/02/2011 10:35 PM, Dan Smith wrote:
> This adds payload support to user-cr for stashing things in the image.
> The first type of payload supported is a transient filesystem image,
> for things like /dev/shm.
>
> When I put "/dev/shm" into args.save_fs[] (and restore_fs), I am able
> to checkpoint and restart programs that are using POSIX sem_* operations
> successfully.

The posix semaphore use the mapped deleted hardlinked files.

...

sem_open("sem.dummy_sem_open", O_CREAT | O_EXCL, 0600, 1);

...

lstat("/dev/shm/sem.zaptW5", 0x7ffff086f530) = -1 ENOENT (No such file 
or directory)
open("/dev/shm/sem.zaptW5", O_RDWR|O_CREAT|O_EXCL, 0600) = 3
write(3, 
"\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 32) = 32
mmap(NULL, 32, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x7f1dda7b3000
link("/dev/shm/sem.zaptW5", "/dev/shm/sem.dummy_sem_open") = 0
fstat(3, {st_mode=S_IFREG|0600, st_size=32, ...}) = 0
brk(0)                                  = 0x238e000
brk(0x23af000)                          = 0x23af000
unlink("/dev/shm/sem.zaptW5")           = 0
close(3)                                = 0

...

AFAIK, the current implementation do not support that, no ?
How is it possible to CR programs using sem_* operations in this case ?

Thanks
   -- Daniel