* KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote: > > On Wed, Sep 15, 2010 at 19:58, Avi Kivity <avi@xxxxxxxxxx> wrote: > > > > > Instead of those two syscalls, how about a vmfd(pid_t pid, ulong start, > > > ulong len) system call which returns an file descriptor that represents a > > > portion of the process address space. You can then use preadv() and > > > pwritev() to copy memory, and io_submit(IO_CMD_PREADV) and > > > io_submit(IO_CMD_PWRITEV) for asynchronous variants (especially useful with > > > a dma engine, since that adds latency). > > > > > > With some care (and use of mmu_notifiers) you can even mmap() your vmfd and > > > access remote process memory directly. > > > > Rather than introducing a new vmfd() API for this, why not just add > > implementations for these more efficient operations to the existing > > /proc/$pid/mem interface? > > As far as I heared from my friend, old HP MPI implementation used > /proc/$pid/mem for this purpose. (I don't know current status). > However almost implementation doesn't do that because /proc/$pid/mem > required the process is ptraced. As far as I understand , very old > /proc/$pid/mem doesn't require it. but It changed for security > concern. Then, Anybody haven't want to change this interface because > they worry break security. > > But, I don't know what exactly protected "the process is ptraced" > check. If anyone explain the reason and we can remove it. I'm not > againt at all. I did some Git digging - that ptrace check for /proc/$pid/mem read/write goes all the way back to the beginning of written human history, aka Linux v2.6.12-rc2. I researched the fragmented history of the stone ages as well, i checked out numerous cave paintings, and while much was lost, i was able to recover this old fragment of a clue in the cave called 'patch-2.3.27', carbon-dated back as far as the previous millenium (!): mem_read() in fs/proc/base.c: + * 1999, Al Viro. Rewritten. Now it covers the whole per-process part. + * Instead of using magical inumbers to determine the kind of object + * we allocate and fill in-core inodes upon lookup. They don't even + * go into icache. We cache the reference to task_struct upon lookup too. + * Eventually it should become a filesystem in its own. We don't use the + * rest of procfs anymore. In such a long timespan language has changed much, so not all of this scribbling can be interpreted - but one thing appears to be sure: this is where the MAY_PTRACE() restriction was introduced to /proc/$pid/mem - as part of a massive rewrite. Alas, the reason for the restriction was not documented, and is feared to be lost forever. Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>