On Tue, 26 Aug 2025, Ian Kent wrote: > On 25/8/25 22:38, Askar Safin wrote: > > ---- On Fri, 22 Aug 2025 16:31:46 +0400 Ian Kent <raven@xxxxxxxxxx> wrote --- > > > On 21/8/25 15:53, Askar Safin wrote: > > > > autofs.rst says: > > > >> mounting onto a directory is considered to be "beyond a `stat`" > > > > in https://elixir.bootlin.com/linux/v6.17-rc2/source/Documentation/filesystems/autofs.rst#L109 > > > > > > > > This is not true. Mounting does not trigger automounts. > > > > > > I don't understand that statement either, it's been many years > > > > Let me explain. > > I do understand what your saying but without more information about > > the meaning and intent of the text your concerned about I don't think > > anything can be done about this right now. Yes, there is definitely something wrong there. I'll try to work out what I really meant to say and propose some alternate wording - hopefully within a week or so. Thanks for raising this Askar, NeilBrown > > > I guess that I should also apologise to you as I'm pretty sure I > > reviewed this at the time it was posted and didn't question this > > at the time. But I most likely didn't see this as a problem because, > > to my thinking, what follows explains what it's needed for rather > > than the earlier statement justifying it. > > > To be clear, in my previous reply I said two things, first I also > > find the statement you are concerned about unclear, perhaps even > > misleading (but I would need to understand the statement original > > intent to interpret that, which I don't) and second, the ->d_namage() > > callback is most definitely needed for the function of the user space > > daemon, automount(8) (via the autofs file system). > > > Ian > > > > > Some syscalls follow (and trigger) automounts in last > > component of path, and some - not. > > > > stat(2) is one of syscalls, which don't follow > > automounts in last component of supplied path. > > > > Many other syscalls do follow automounts. > > > > autofs.rst calls syscalls, which follow automounts, > > as "beyond a stat". > > > > Notably mount(2) doesn't follow automounts in second argument > > (i. e. mountpoint). I know this, because I closely did read the code. > > Also I did experiment (see source in the end of this letter). > > Experiment was on 6.17-rc1. > > > > But "autofs.rst" says: > >> mounting onto a directory is considered to be "beyond a `stat`" > > I. e. "autofs.rst" says that mount(2) does follow automounts. > > > > This is wrong, as I explained above. (Again: I did experiment, > > so I'm totally sure that this "autofs.rst" sentence is wrong.) > > > > Moreover, then "autofs.rst" proceeds to explain why > > DCACHE_MANAGE_TRANSIT was introduced, based on this wrong fact. > > > > So it is possible that DCACHE_MANAGE_TRANSIT is in fact, not needed. > > > > I'm not asking for removal of DCACHE_MANAGE_TRANSIT. > > > > I merely point error in autofs.rst file and ask for fix. > > > > And if in process of fixing autofs.rst you will notice that > > DCACHE_MANAGE_TRANSIT is indeed not needed, then, > > of course, it should be removed. > > > > -- > > Askar Safin > > https://types.pl/@safinaskar > > > > ==== > > > > // This code is public domain > > // You should be root in initial user namespace > > > > #define _GNU_SOURCE > > > > #include <stdio.h> > > #include <stdlib.h> > > #include <stdbool.h> > > #include <string.h> > > #include <unistd.h> > > #include <fcntl.h> > > #include <sched.h> > > #include <errno.h> > > #include <sys/stat.h> > > #include <sys/mount.h> > > #include <sys/syscall.h> > > #include <sys/vfs.h> > > #include <sys/sysmacros.h> > > #include <sys/statvfs.h> > > #include <sys/wait.h> > > #include <linux/openat2.h> > > #include <linux/nsfs.h> > > > > #define MY_ASSERT(cond) do { \ > > if (!(cond)) { \ > > fprintf (stderr, "%d: %s: assertion failed\n", __LINE__, #cond); \ > > exit (1); \ > > } \ > > } while (0) > > > > #define MY_ASSERT_ERRNO(cond) do { \ > > if (!(cond)) { \ > > fprintf (stderr, "%d: %s: %m\n", __LINE__, #cond); \ > > exit (1); \ > > } \ > > } while (0) > > > > static void > > mount_debugfs (void) > > { > > if (mount (NULL, "/tmp/debugfs", "debugfs", 0, NULL) != 0) > > { > > perror ("mount debugfs"); > > exit (1); > > } > > } > > > > int > > main (void) > > { > > MY_ASSERT_ERRNO (chdir ("/") == 0); > > MY_ASSERT_ERRNO (unshare (CLONE_NEWNS) == 0); > > MY_ASSERT_ERRNO (mount (NULL, "/", NULL, MS_PRIVATE | MS_REC, NULL) == 0); > > MY_ASSERT_ERRNO (mount (NULL, "/tmp", "tmpfs", 0, NULL) == 0); > > MY_ASSERT_ERRNO (mkdir ("/tmp/debugfs", 0777) == 0); > > mount_debugfs (); > > MY_ASSERT_ERRNO (mount (NULL, "/tmp/debugfs/tracing", "tmpfs", 0, NULL) == 0); > > execlp ("/bin/busybox", "sh", NULL); > > MY_ASSERT (false); > > } > > >
