On Wed, Jun 07, 2006 at 05:10:14PM -0700, Dave Hansen wrote:
>
> This allows a vfsmount to keep track of how many instances
> of files open for write there are at a given time. This
> will be useful if it is ever desired to change a mount
> from r/w to r/o at runtime.
>
> A mount can also potentially refuse to allow writers; this
> is why mnt_want_write() has a return value. However, that
> functionality will be added later in the series. For now,
> always allow new writers.
>
> Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
> ---
>
> lxc-dave/fs/namespace.c | 1 +
> lxc-dave/include/linux/mount.h | 14 ++++++++++++++
> 2 files changed, 15 insertions(+)
>
> diff -puN fs/namespace.c~convert-permission-to-file-and-vfs fs/namespace.c
> --- lxc/fs/namespace.c~convert-permission-to-file-and-vfs 2006-06-07 16:53:11.000000000 -0700
> +++ lxc-dave/fs/namespace.c 2006-06-07 16:53:11.000000000 -0700
> @@ -66,6 +66,7 @@ struct vfsmount *alloc_vfsmnt(const char
> if (mnt) {
> memset(mnt, 0, sizeof(struct vfsmount));
> atomic_set(&mnt->mnt_count, 1);
> + /* atomic_set(&mnt->writer_count, 0); */
IMHO you should not assume that atomic_set(,0) will not
be required after memset(,0,), so doing it here is the
right thing (tm)
> INIT_LIST_HEAD(&mnt->mnt_hash);
> INIT_LIST_HEAD(&mnt->mnt_child);
> INIT_LIST_HEAD(&mnt->mnt_mounts);
> diff -puN include/linux/mount.h~convert-permission-to-file-and-vfs include/linux/mount.h
> --- lxc/include/linux/mount.h~convert-permission-to-file-and-vfs 2006-06-07 16:53:11.000000000 -0700
> +++ lxc-dave/include/linux/mount.h 2006-06-07 16:53:11.000000000 -0700
> @@ -12,6 +12,8 @@
> #define _LINUX_MOUNT_H
> #ifdef __KERNEL__
>
> +#include <linux/err.h>
> +#include <linux/fs.h>
> #include <linux/types.h>
> #include <linux/list.h>
> #include <linux/spinlock.h>
> @@ -38,6 +40,7 @@ struct vfsmount {
> struct list_head mnt_mounts; /* list of children, anchored here */
> struct list_head mnt_child; /* and going through their mnt_child */
> atomic_t mnt_count;
> + atomic_t mnt_writers;
> int mnt_flags;
> int mnt_expiry_mark; /* true if marked for expiry */
> char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */
> @@ -58,6 +61,17 @@ static inline struct vfsmount *mntget(st
> return mnt;
> }
>
> +static inline int mnt_want_write(struct vfsmount *mnt)
> +{
> + atomic_inc(&mnt->mnt_writers);
> + return 0;
> +}
> +
> +static inline void mnt_drop_write(struct vfsmount *mnt)
> +{
> + atomic_dec(&mnt->mnt_writers);
> +}
> +
> extern void mntput_no_expire(struct vfsmount *mnt);
> extern void mnt_pin(struct vfsmount *mnt);
> extern void mnt_unpin(struct vfsmount *mnt);
> diff -L convert-permission-to-file-and-vfs -puN /dev/null /dev/null
> diff -L convert-permission-to-file-and-vfs.patch -puN /dev/null /dev/null
> _
best,
Herbert
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