On Mon, Aug 21 2017, Ian Kent wrote: >> >> A mount isn't triggered by kern_path(pathname, 0, &path). >> That '0' would need to include one of >> LOOKUP_PARENT | LOOKUP_DIRECTORY | >> LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT >> >> to trigger an automount (otherwise you just get -EISDIR). > > It's perfectly sensible to think that but there is a case where a > a mount is triggered when using kern_path(). > > The EISDIR return occurs for positive dentrys, negative dentrys > will still trigger an automount (which is autofs specific, > indirect mount map using nobrowse option, the install default).
Ok, I understand this better now. This difference between direct and indirect mounts is slightly awkward. It is visible from user-space, but not elegant to document. When you use O_PATH to open a direct automount that has not already been triggered, the open returns the underlying directory (and fstatfs confirms that it is AUTOFS_SUPER_MAGIC). When you use O_PATH on an indirect automount, it *will* trigger the automount when "nobrowse" is in effect, but it won't when "browse" is in effect. So we cannot just say "O_PATH doesn't trigger automounts", which is essentially what I said in https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=97a45d02e6671482e8b2cdcce3951930bf6bdb94 It might be possible to modify automount so that it was more consistent - i.e. if the point is triggered by a mkdir has been done, just to the mkdir. If it is triggered after a mkdir has been done, do the mount. I guess that might be racy, and in any case is hard to justify. Maybe I should change it to be about "direct automounts", and add a note that indirect automounts aren't so predictable. But back to my original issue of wanting to discard kern_path_mountpoint, what would you think of the following approach - slight revised from before. Thanks, NeilBrown diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index beef981aa54f..7663ea82e68d 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -135,10 +135,13 @@ static inline struct autofs_info *autofs4_dentry_ino(struct dentry *dentry) /* autofs4_oz_mode(): do we see the man behind the curtain? (The * processes which do manipulations for us in user space sees the raw * filesystem without "magic".) + * A process performing certain ioctls can get temporary oz status. */ +extern struct task_struct *autofs_tmp_oz; static inline int autofs4_oz_mode(struct autofs_sb_info *sbi) { - return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp; + return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp || + autofs_tmp_oz == current; } struct inode *autofs4_get_inode(struct super_block *, umode_t); diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c index dd9f1bebb5a3..d76401669a20 100644 --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -200,6 +200,20 @@ static int autofs_dev_ioctl_protosubver(struct file *fp, return 0; } +struct task_struct *autofs_tmp_oz; +int kern_path_oz(const char *pathname, int flags, struct path *path) +{ + static DEFINE_MUTEX(autofs_oz); + int err; + + mutex_lock(&autofs_oz); + autofs_tmp_oz = current; + err = kern_path(pathname, flags, path); + autofs_tmp_oz = NULL; + mutex_unlock(&autofs_oz); + return err; +} + /* Find the topmost mount satisfying test() */ static int find_autofs_mount(const char *pathname, struct path *res, @@ -209,7 +223,8 @@ static int find_autofs_mount(const char *pathname, struct path path; int err; - err = kern_path_mountpoint(AT_FDCWD, pathname, &path, 0); + err = kern_path_oz(pathname, 0, &path); + if (err) return err; err = -ENOENT; @@ -552,8 +567,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp, if (!fp || param->ioctlfd == -1) { if (autofs_type_any(type)) - err = kern_path_mountpoint(AT_FDCWD, - name, &path, LOOKUP_FOLLOW); + err = kern_path_oz(name, LOOKUP_FOLLOW, &path); else err = find_autofs_mount(name, &path, test_by_type, &type);
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