Hi, in criu we intensively use additional information provided by /proc/<pid>/fdinfo/<fd> particular to the object opened file represents. The output is printed out by calling the file_operations::show_fdinfo method.
The implementation implies that data is getting printed in one pass and returns error in case if seq buffer is overflowed, which works fine while data fit one memory page. For epoll it's about 73 epoll targets can be printed, for notify system -- significantly less depending on notify type and file handler. This limitation didn't cause any problems in applications we're checkpointing and restoring at moment, but might become a problem in future. So to resolve the problem I considered two ways 1) Don't return error if seq-buffer overflowed thus, one show() method is called the kernel will notice that buffer is overflowed and double its size returning -EAGAIN. But I fear such interface might be misused (say process creates epoll with a number of target descriptors, then application opens a big number of fdinfo reader causing kernel to allocate big seq-buffer for each reader). 2) Instead of printing fdinfo in one pass rather provide seq-operations pointer in file_operations, and subsystems which need it simply hook own seq-operations here. The main code in fs/proc/fd.c will call for underlied seq-operation methods. The second way looks more preferrable from my POV, here is the series. Please take a look, thanks. Any comments are highly appreciated! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
