Messages in this thread | | | Date | Mon, 07 Nov 2011 15:49:17 +0100 | From | Davidlohr Bueso <> | Subject | Re: [RFC PATCH] tmpfs: support user quotas |
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On Mon, 2011-11-07 at 04:11 -0500, Valdis.Kletnieks@vt.edu wrote: > On Sun, 06 Nov 2011 18:15:01 -0300, Davidlohr Bueso said: > > > @@ -1159,7 +1159,12 @@ shmem_write_begin(struct file *file, struct address_space *mapping, > > struct page **pagep, void **fsdata) > > > + if (atomic_long_read(&user->shmem_bytes) + len > > > + rlimit(RLIMIT_TMPFSQUOTA)) > > + return -ENOSPC; > > Is this a per-process or per-user limit? If it's per-process, it doesn't > really do much good, because a user can use multiple processes to over-run the > limit (either intentionally or accidentally).
This is a per-user limit. > > > @@ -1169,10 +1174,12 @@ shmem_write_end(struct file *file, struct address_space *mapping, > > struct page *page, void *fsdata) > > > + if (pos + copied > inode->i_size) { > > i_size_write(inode, pos + copied); > > + atomic_long_add(copied, &user->shmem_bytes); > > + } > If this is per-user, it's racy with shmem_write_begin() - two processes can hit > the write_begin(), be under quota by (say) 1M, but by the time they both > complete the user is 1M over the quota. > I guess using a spinlock instead of atomic operations would serve the purpose.
> > @@ -1535,12 +1542,15 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry) > > + struct user_struct *user = current_user(); > > + atomic_long_sub(inode->i_size, &user->shmem_bytes); > > What happens here if user 'fred' creates a file on a tmpfs, and then logs out so he has > no processes running, and then root does a 'find tmpfs -user fred -exec rm {} \;' to clean up? > We just decremented root's quota, not fred's.... > Would the same would occur with mqueues? I haven't tested it but I don't see anywhere that user->mq_bytes is decreased like this.
Thanks, Davidlohr
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