[patch 20/21] vfs: no "(unreachable)" prefix for SYSVIPC maps in /proc/PID/maps

[patch 20/21] vfs: no "(unreachable)" prefix for SYSVIPC maps in /proc/PID/maps

[akpm]

From: Miklos Szeredi <mszeredi@suse.cz>

The patch

  "vfs: fix d_path() for unreachable paths"

generally changed d_path() to report unreachable paths with a special
prefix.  This has an effect on /proc/${PID}/maps as well for memory maps
set up with shmem_file_setup() or hugetlb_file_setup().  These functions
set up unlinked files under a kernel-private vfsmount.  Since this
vfsmount is unreachable from userspace, these maps will be reported with
the "(unreachable)" prefix.

This is undesirable, because it changes the kernel ABI and might break
applications for no good reason.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Andreas Gruenbacher <agruen@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/hugetlbfs/inode.c |   17 +++++++++++++++++
 mm/shmem.c           |   17 +++++++++++++++++
 2 files changed, 34 insertions(+)

diff -puN fs/hugetlbfs/inode.c~vfs-no-unreachable-prefix-for-sysvipc-maps-in-proc-pid-maps fs/hugetlbfs/inode.c
--- a/fs/hugetlbfs/inode.c~vfs-no-unreachable-prefix-for-sysvipc-maps-in-proc-pid-maps
+++ a/fs/hugetlbfs/inode.c
@@ -906,6 +906,21 @@ static struct file_system_type hugetlbfs
 
 static struct vfsmount *hugetlbfs_vfsmount;
 
+/*
+ * Do a special d_dname function so that these are not prefixed by
+ * "(unreachable)".
+ */
+static char *hugetlb_unlinked_d_dname(struct dentry *dentry, char *buf,
+				      int buflen)
+{
+	return dynamic_dname(dentry, buf, buflen, "/%s (deleted)",
+			     dentry->d_name.name);
+}
+
+static struct dentry_operations hugetlb_unlinked_dentry_operations = {
+	.d_dname = hugetlb_unlinked_d_dname,
+};
+
 static int can_do_hugetlb_shm(void)
 {
 	return capable(CAP_IPC_LOCK) || in_group_p(sysctl_hugetlb_shm_group);
@@ -943,6 +958,8 @@ struct file *hugetlb_file_setup(const ch
 	if (!dentry)
 		goto out_shm_unlock;
 
+	dentry->d_op = &hugetlb_unlinked_dentry_operations;
+
 	error = -ENOSPC;
 	inode = hugetlbfs_get_inode(root->d_sb, current_fsuid(),
 				current_fsgid(), S_IFREG | S_IRWXUGO, 0);
diff -puN mm/shmem.c~vfs-no-unreachable-prefix-for-sysvipc-maps-in-proc-pid-maps mm/shmem.c
--- a/mm/shmem.c~vfs-no-unreachable-prefix-for-sysvipc-maps-in-proc-pid-maps
+++ a/mm/shmem.c
@@ -2602,6 +2602,21 @@ int shmem_unuse(swp_entry_t entry, struc
 
 /* common code */
 
+/*
+ * Do a special d_dname function so that these are not prefixed by
+ * "(unreachable)".
+ */
+static char *shmem_unlinked_d_dname(struct dentry *dentry, char *buf,
+				    int buflen)
+{
+	return dynamic_dname(dentry, buf, buflen, "/%s (deleted)",
+			     dentry->d_name.name);
+}
+
+static struct dentry_operations shmem_unlinked_dentry_operations = {
+	.d_dname = shmem_unlinked_d_dname,
+};
+
 /**
  * shmem_file_setup - get an unlinked file living in tmpfs
  * @name: name for dentry (to be seen in /proc/<pid>/maps
@@ -2634,6 +2649,8 @@ struct file *shmem_file_setup(const char
 	if (!dentry)
 		goto put_memory;
 
+	dentry->d_op = &shmem_unlinked_dentry_operations;
+
 	error = -ENFILE;
 	file = get_empty_filp();
 	if (!file)
_

Re: [patch 20/21] vfs: no "(unreachable)" prefix for SYSVIPC maps in /proc/PID/maps

[Al Viro]

On Fri, Sep 18, 2009 at 01:06:02PM -0700, akpm@linux-foundation.org wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> The patch
> 
>   "vfs: fix d_path() for unreachable paths"
> 
> generally changed d_path() to report unreachable paths with a special
> prefix.  This has an effect on /proc/${PID}/maps as well for memory maps
> set up with shmem_file_setup() or hugetlb_file_setup().  These functions
> set up unlinked files under a kernel-private vfsmount.  Since this
> vfsmount is unreachable from userspace, these maps will be reported with
> the "(unreachable)" prefix.
> 
> This is undesirable, because it changes the kernel ABI and might break
> applications for no good reason.

I'd rather see 17, 19 and 20 collapsed...

Re: [patch 20/21] vfs: no "(unreachable)" prefix for SYSVIPC maps in /proc/PID/maps

[Al Viro]

On Mon, Sep 21, 2009 at 11:04:51AM +0100, Al Viro wrote:

> I'd rather see 17, 19 and 20 collapsed...

D'oh - s/17/16/ in the above.  IOW, d_path() patch + these two fixups
to it.