On Mon, May 22, 2017 at 08:16:36AM +1000, NeilBrown wrote:
> oooh... it just occurred to me that for a mount, I can make it
> read/write by:
>
> mount -o remount,rw none /mount/point
>
> providing I know that no other flags are needed. I don't need to give
> the correct device path, do I?
Yes, "none" is an usable placeholder there.
> > After this call, mount reads fstab and merges these options with the
> > options from the command line (-o). If no mountpoint is found in
> > fstab, then a remount with unspecified source is allowed.
>
> BTW, if fstab contains just
>
> /bar /foo none bind 0 0
>
>
> Then both
> mount -o remount,rw /bar
> and
> mount -o remount,rw /foo
>
> will try to remount /foo. This is also surprising....
Yes, mount(8) goal is to accept "whatever" to keep users happy :-)
This your example is well known disadvantage, the solution is to use
--source and --target options (it's strongly recommended for scripts):
mount -o remount,rw --source /bar
mount -o remount,rw --target /foo
in this case mount(8) will not try to be smart...
...
> >> You could possibly argue that the current behaviour is correct
> >> as /foo is listed as bind mount. That doesn't stop is being surprising.
> >> Also
> >> mount /bar /foo -o remount,rw
> >>
> >> doesn't pick up the "bind" flag, so the filesystem gets remounted.
> >> So I think there is definitely something wrong.
> >
> > That's question... "remount,bind" is really special and maybe "bind"
> > from fstab should be really ignored in this case.
>
> I think that is probably the best way forward, at least in the short
> term.
> I might try to dig into the code and see how easy this would be.
It's trivial patch, see below. Seems to work as expected (I use
"findmnt -o TARGET,VFS-OPTIONS,FS-OPTION" to see ro/rw).
Karel
diff --git a/libmount/src/context.c b/libmount/src/context.c
index 38e0363..a574758 100644
--- a/libmount/src/context.c
+++ b/libmount/src/context.c
@@ -2038,7 +2038,7 @@ static int apply_table(struct libmnt_context *cxt, struct libmnt_table *tb,
*/
int mnt_context_apply_fstab(struct libmnt_context *cxt)
{
- int rc = -1, isremount = 0;
+ int rc = -1, isremount = 0, iscmdbind = 0;
struct libmnt_table *tab = NULL;
const char *src = NULL, *tgt = NULL;
unsigned long mflags = 0;
@@ -2063,8 +2063,10 @@ int mnt_context_apply_fstab(struct libmnt_context *cxt)
cxt->optsmode &= ~MNT_OMODE_FORCE;
}
- if (mnt_context_get_mflags(cxt, &mflags) == 0 && mflags & MS_REMOUNT)
- isremount = 1;
+ if (mnt_context_get_mflags(cxt, &mflags) == 0) {
+ isremount = !!(mflags & MS_REMOUNT);
+ iscmdbind = !!(mflags & MS_BIND);
+ }
if (cxt->fs) {
src = mnt_fs_get_source(cxt->fs);
@@ -2131,6 +2133,12 @@ int mnt_context_apply_fstab(struct libmnt_context *cxt)
* not found are not so important and may be misinterpreted by
* applications... */
rc = -MNT_ERR_NOFSTAB;
+
+
+ } else if (isremount && !iscmdbind) {
+
+ /* remove "bind" from fstab (or no-op if not present) */
+ mnt_optstr_remove_option(&cxt->fs->optstr, "bind");
}
return rc;
}
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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