Seems worth a shot. May get shot down by Al or someone, but it
seems a good place to start.
There may be opposition to the name, 'special', being too generic,
but I can't think of a better name (never_linked, ...)
-serge
Quoting Oren Laadan (orenl@xxxxxxxxxxxxxxx):
> Commit a3a065e3f13da8a3470ed09c7f38aad256083726 changes the behavior
> of dentry for pipe, sockets and anon_inodes (eventfd, timerfd, epoll,
> signalfd and perf...):
>
> """
> Filesystems outside the regular namespace do not have to clear
> in order to have a working /proc/$pid/fd/XXX. Nothing in proc prevents the
> fd link from being used if its dentry is not in the hash.
>
> Also, it does not get put into the dcache hash if DCACHE_UNHASHED is clear;
> that depends on the filesystem calling d_add or d_rehash.
>
> So delete the misleading comments and needless code.
> """
>
> That made checkpoint complain on half-closed pipes which are
> DCACHE_UNHASHED and trigger the d_unlinked() test.
>
> This patch proposes one fix - which is to mark such dentry with a
> special flag DCACHE_SPECIAL_INODE, which indicates that this dentry
> is an exception, and the d_unlinked() doesn't matter.
>
> An alternative approach would be to add an unlinked() method to file
> operations: if it's null, then checkpoint will test with d_unlinked()
> otherwise it will test with the specific method. for these filesystems
> we'll make this method return "ok" always. This may also be useful if
> unlinking a file becomes a per-filesystem operation.
>
> Comments ?
>
>
> Oren.
>
>
> ---
> checkpoint/files.c | 2 +-
> fs/anon_inodes.c | 1 +
> fs/pipe.c | 1 +
> include/linux/dcache.h | 14 +++++++++++++-
> net/socket.c | 1 +
> 5 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/checkpoint/files.c b/checkpoint/files.c
> index d1242f2..fa318f3 100644
> --- a/checkpoint/files.c
> +++ b/checkpoint/files.c
> @@ -231,7 +231,7 @@ int checkpoint_file(struct ckpt_ctx *ctx, void *ptr)
> file, file->f_op);
> return -EBADF;
> }
> - if (d_unlinked(file->f_dentry)) {
> + if (!d_special_inode(file->f_dentry) && d_unlinked(file->f_dentry)) {
> ckpt_err(ctx, -EBADF, "%(T)%(P)Unlinked files unsupported\n",
> file);
> return -EBADF;
> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 9f0bf13..a7bf417 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -118,6 +118,7 @@ struct file *anon_inode_getfile(const char *name,
> atomic_inc(&anon_inode_inode->i_count);
>
> path.dentry->d_op = &anon_inodefs_dentry_operations;
> + path.dentry->d_flags |= DCACHE_SPECIAL_INODE;
> d_instantiate(path.dentry, anon_inode_inode);
>
> error = -ENFILE;
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 8c79493..2fd5ad6 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1213,6 +1213,7 @@ struct file *create_write_pipe(int flags)
> path.mnt = mntget(pipe_mnt);
>
> path.dentry->d_op = &pipefs_dentry_operations;
> + path.dentry->d_flags |= DCACHE_SPECIAL_INODE;
> d_instantiate(path.dentry, inode);
>
> err = -ENFILE;
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index 30b93b2..af01318 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -186,6 +186,13 @@ d_iput: no no no yes
>
> #define DCACHE_FSNOTIFY_PARENT_WATCHED 0x0080 /* Parent inode is watched by some fsnotify listener */
>
> +#define DCACHE_SPECIAL_INODE 0x0100
> + /* This dentry corresponds to a special inode, like anon-inode,
> + * pipe, and sockets. It is set once by the file-system. Used by
> + * checkpoint/restart to ignore a positive d_unlinked() for such
> + * dentries (a closed pipe is not a unlinked file)
> + */
> +
> extern spinlock_t dcache_lock;
> extern seqlock_t rename_lock;
>
> @@ -347,7 +354,12 @@ extern struct dentry * dget_locked(struct dentry *);
> *
> * Returns true if the dentry passed is not currently hashed.
> */
> -
> +
> +static inline int d_special_inode(struct dentry *dentry)
> +{
> + return (dentry->d_flags & DCACHE_SPECIAL_INODE);
> +}
> +
> static inline int d_unhashed(struct dentry *dentry)
> {
> return (dentry->d_flags & DCACHE_UNHASHED);
> diff --git a/net/socket.c b/net/socket.c
> index 3253c04..dd5983a 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -365,6 +365,7 @@ int sock_alloc_file(struct socket *sock, struct file **f, int flags)
> path.mnt = mntget(sock_mnt);
>
> path.dentry->d_op = &sockfs_dentry_operations;
> + path.dentry->d_flags |= DCACHE_SPECIAL_INODE;
> d_instantiate(path.dentry, SOCK_INODE(sock));
> SOCK_INODE(sock)->i_fop = &socket_file_ops;
>
> --
> 1.6.3.3
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