[Devel] Re: [PATCH] [RFC] Checkpoint/restart eventfd

[Serge E. Hallyn]

Quoting Matt Helsley (matthltc at us.ibm.com):
> Save/restore eventfd files. These are anon_inodes just like epoll
> but instead of a set of files to poll they are a 64-bit counter
> and a flag value. Used for AIO.
> 
> Signed-off-by: Matt Helsley <matthltc at us.ibm.com>
> 
> NOTE: Marked [RFC] because it strangely does not pass my adapted LTP
> 	test cases unless it's running from a checkpointed image.
> 	Seems to be a mistake in the test case adaptation.
> ---
>  checkpoint/files.c             |    7 +++++
>  fs/eventfd.c                   |   51 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/checkpoint_hdr.h |    8 ++++++
>  include/linux/eventfd.h        |   10 ++++++++
>  4 files changed, 76 insertions(+), 0 deletions(-)
> 
> diff --git a/checkpoint/files.c b/checkpoint/files.c
> index f6de07e..43b95cc 100644
> --- a/checkpoint/files.c
> +++ b/checkpoint/files.c
> @@ -23,6 +23,7 @@
>  #include <linux/checkpoint.h>
>  #include <linux/checkpoint_hdr.h>
>  #include <net/sock.h>
> +#include <linux/eventfd.h>
> 
> 
>  /**************************************************************************
> @@ -607,6 +608,12 @@ static struct restore_file_ops restore_file_ops[] = {
>  		.file_type = CKPT_FILE_TTY,
>  		.restore = tty_file_restore,
>  	},
> +	/* eventfd */
> +	{
> +		.file_name = "EVENTFD",
> +		.file_type = CKPT_FILE_EVENTFD,
> +		.restore = eventfd_restore,
> +	},
>  };
> 
>  static struct file *do_restore_file(struct ckpt_ctx *ctx)
> diff --git a/fs/eventfd.c b/fs/eventfd.c
> index 31d12de..5d30cd5 100644
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -18,6 +18,8 @@
>  #include <linux/module.h>
>  #include <linux/kref.h>
>  #include <linux/eventfd.h>
> +#include <linux/checkpoint.h>
> +#include <linux/checkpoint_hdr.h>
> 
>  struct eventfd_ctx {
>  	struct kref kref;
> @@ -223,11 +225,34 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
>  	return res;
>  }
> 
> +static int eventfd_checkpoint(struct ckpt_ctx *ckpt_ctx, struct file *file)
> +{
> +	struct eventfd_ctx *ctx;
> +	struct ckpt_hdr_file_eventfd *h;
> +	int ret = -ENOMEM;
> +
> +	h = ckpt_hdr_get_type(ckpt_ctx, sizeof(*h), CKPT_HDR_FILE);
> +	if (!h)
> +		return -ENOMEM;
> +	h->common.f_type = CKPT_FILE_EVENTFD;
> +	ret = checkpoint_file_common(ckpt_ctx, file, &h->common);
> +	if (ret < 0)
> +		goto out;
> +	ctx = file->private_data;
> +	h->count = ctx->count;

I only took a very cursory glance at the eventfd code, but eventfd_poll()
suggests that ULLONG_MAX is a valid value for ctx->count (suggesting error).
Should you be checking for that?  (Or is that a special case that will
never be checkpointed somehow?)

> +	h->flags = ctx->flags;
> +	ret = ckpt_write_obj(ckpt_ctx, &h->common.h);
> +out:
> +	ckpt_hdr_put(ckpt_ctx, h);
> +	return ret;
> +}
> +
>  static const struct file_operations eventfd_fops = {
>  	.release	= eventfd_release,
>  	.poll		= eventfd_poll,
>  	.read		= eventfd_read,
>  	.write		= eventfd_write,
> +	.checkpoint     = eventfd_checkpoint,
>  };
> 
>  /**
> @@ -335,3 +360,29 @@ SYSCALL_DEFINE1(eventfd, unsigned int, count)
>  	return sys_eventfd2(count, 0);
>  }
> 
> +struct file *eventfd_restore(struct ckpt_ctx *ckpt_ctx,
> +			     struct ckpt_hdr_file *ptr)
> +{
> +	struct ckpt_hdr_file_eventfd *h = (struct ckpt_hdr_file_eventfd *)ptr;
> +	struct file *evfile;
> +	int evfd, ret;
> +
> +	/* Already know type == CKPT_HDR_FILE and f_type == CKPT_FILE_EVENTFD */
> +	if (h->common.h.len != sizeof(*h))
> +		return ERR_PTR(-EINVAL);
> +
> +	evfd = sys_eventfd2(h->count, h->flags);
> +	if (evfd < 0)
> +		return ERR_PTR(evfd);
> +	evfile = fget(evfd);
> +	sys_close(evfd);
> +	if (!evfile)
> +		return ERR_PTR(-EBUSY);
> +
> +	ret = restore_file_common(ckpt_ctx, evfile, &h->common);
> +	if (ret < 0) {
> +		fput(evfile);
> +		return ERR_PTR(ret);
> +	}
> +	return evfile;
> +}
> diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
> index ff2e4aa..dc22244 100644
> --- a/include/linux/checkpoint_hdr.h
> +++ b/include/linux/checkpoint_hdr.h
> @@ -476,6 +476,8 @@ enum file_type {
>  #define CKPT_FILE_SOCKET CKPT_FILE_SOCKET
>  	CKPT_FILE_TTY,
>  #define CKPT_FILE_TTY CKPT_FILE_TTY
> +	CKPT_FILE_EVENTFD,
> +#define CKPT_FILE_EVENTFD CKPT_FILE_EVENTFD
>  	CKPT_FILE_MAX
>  #define CKPT_FILE_MAX CKPT_FILE_MAX
>  };
> @@ -500,6 +502,12 @@ struct ckpt_hdr_file_pipe {
>  	__s32 pipe_objref;
>  } __attribute__((aligned(8)));
> 
> +struct ckpt_hdr_file_eventfd {
> +	struct ckpt_hdr_file common;
> +	__u64 count;
> +	__u32 flags;
> +} __attribute__((aligned(8)));
> +
>  /* socket */
>  struct ckpt_hdr_socket {
>  	struct ckpt_hdr h;
> diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
> index 3b85ba6..a904633 100644
> --- a/include/linux/eventfd.h
> +++ b/include/linux/eventfd.h
> @@ -34,6 +34,15 @@ struct eventfd_ctx *eventfd_ctx_fdget(int fd);
>  struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
>  int eventfd_signal(struct eventfd_ctx *ctx, int n);
> 
> +#ifdef CONFIG_CHECKPOINT
> +struct ckpt_ctx;
> +struct ckpt_hdr_file;
> +
> +struct file *eventfd_restore(struct ckpt_ctx *ckpt_ctx,
> +			     struct ckpt_hdr_file *ptr);
> +#else
> +#define eventfd_restore NULL
> +#endif
>  #else /* CONFIG_EVENTFD */
> 
>  /*
> @@ -55,6 +64,7 @@ static inline void eventfd_ctx_put(struct eventfd_ctx *ctx)
> 
>  }
> 
> +#define eventfd_restore NULL
>  #endif
> 
>  #endif /* _LINUX_EVENTFD_H */
> -- 
> 1.5.6.3
> 
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