How does EXT4 ensures two processes don't modify and synchronize one page at the same time.

How does EXT4 ensures two processes don't modify and synchronize one page at the same time.

[Lyu Tao]

Hi,

I'm new to file system area and have a naive question about the global sync.

Let's suppose there are two process are writing to the same file. If one process issues a sync() syscall, which mechanism can ensures the two processes don't modify and synchronize one page at the same time.

Best,
Tao

Re: How does EXT4 ensures two processes don't modify and synchronize one page at the same time.

[Theodore Y. Ts'o]

On Mon, Jan 24, 2022 at 05:17:34PM +0000, Lyu Tao wrote:
> 
> I'm new to file system area and have a naive question about the global sync.
> 
> Let's suppose there are two process are writing to the same file. If
> one process issues a sync() syscall, which mechanism can ensures the
> two processes don't modify and synchronize one page at the same
> time.

That's not what the sync() system call purports to do.  To quote from
the sync(2) man page:

       sync() causes all pending modifications to filesystem metadata
       and cached file data to be written to the underlying
       filesystems.

						- Ted