Messages in this thread | | | Subject | Re: [PATCH] Add pidfs filesystem | From | Pavel Emelyanov <> | Date | Wed, 22 Feb 2017 10:40:49 +0300 |
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On 02/21/2017 05:57 PM, Oleg Nesterov wrote: > 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?
Yes!!! If this whole effort with pidfs and overlayfs will move forward, I would prefer seeing the nodev procfs version, rather than another fs.
As far as the overlayfs part is concerned, having an overlayfs mounted on /proc inside container may result in problems as applications sometimes check for /proc containing procfs (by checking statfs.f_type == PROC_SUPER_MAGIC or by reading the /proc/mounts).
-- Pavel
> 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 > > . >
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