On 02/18, Alexey Gladkov wrote:
>
> This patch allows to mount only the part of /proc related to pids
> without rest objects. Since this is an addon to /proc, flags applied to
> /proc have an effect on this pidfs filesystem.
I leave this to you and Eric, but imo it would be nice to avoid another
filesystem.
> Why not implement it as another flag to /proc ?
>
> The /proc flags is stored in the pid_namespace and are global for
> namespace. It means that if you add a flag to hide all except the pids,
> then it will act on all mounted instances of /proc.
But perhaps we can use mnt_flags? For example, lets abuse MNT_NODEV, see
the simple patch below. Not sure it is correct/complete, just to illustrate
the idea.
With this patch you can mount proc with -onodev and it will only show
pids/self/thread_self:
# mkdir /tmp/D
# mount -t proc -o nodev none /tmp/D
# ls /tmp/D
1 11 13 15 17 19 20 22 24 28 3 31 33 4 56 7 9
thread-self
10 12 14 16 18 2 21 23 27 29 30 32 34 5 6 8 self
# cat /tmp/D/meminfo
cat: /tmp/D/meminfo: No such file or directory
# ls /tmp/D/irq
ls: cannot open directory /tmp/D/irq: No such file or directory
No?
Oleg.
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -305,11 +305,22 @@ int proc_readdir_de(struct proc_dir_entry *de, struct
file *file,
int proc_readdir(struct file *file, struct dir_context *ctx)
{
+ int mnt_flags = file->f_path.mnt->mnt_flags;
struct inode *inode = file_inode(file);
+ if (mnt_flags & MNT_NODEV)
+ return 1;
+
return proc_readdir_de(PDE(inode), file, ctx);
}
+static int proc_dir_open(struct inode *inode, struct file *file)
+{
+ if (file->f_path.mnt->mnt_flags & MNT_NODEV)
+ return -ENOENT;
+ return 0;
+}
+
/*
* These are the generic /proc directory operations. They
* use the in-memory "struct proc_dir_entry" tree to parse
@@ -319,6 +330,7 @@ static const struct file_operations proc_dir_operations = {
.llseek = generic_file_llseek,
.read = generic_read_dir,
.iterate_shared = proc_readdir,
+ .open = proc_dir_open,
};
/*
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -318,12 +318,16 @@ proc_reg_get_unmapped_area(struct file *file, unsigned
long orig_addr,
static int proc_reg_open(struct inode *inode, struct file *file)
{
+ int mnt_flags = file->f_path.mnt->mnt_flags;
struct proc_dir_entry *pde = PDE(inode);
int rv = 0;
int (*open)(struct inode *, struct file *);
int (*release)(struct inode *, struct file *);
struct pde_opener *pdeo;
+ if (mnt_flags & MNT_NODEV)
+ return -ENOENT;
+
/*
* Ensure that
* 1) PDE's ->release hook will be called no matter what
