[Devel] Re: [RFC v5][PATCH 9/9] Restore open file descriprtors

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at cs.columbia.edu):
>
>
> Serge E. Hallyn wrote:
>> Quoting Oren Laadan (orenl at cs.columbia.edu):
>>> Restore open file descriptors: for each FD read 'struct cr_hdr_fd_ent'
>>> and lookup objref in the hash table; if not found (first occurence), read
>>> in 'struct cr_hdr_fd_data', create a new FD and register in the hash.
>>> Otherwise attach the file pointer from the hash as an FD.
>>>
>>> This patch only handles basic FDs - regular files, directories and also
>>> symbolic links.
>>>
>>> Signed-off-by: Oren Laadan <orenl at cs.columbia.edu>
>>> ---
>>>  checkpoint/Makefile        |    2 +-
>>>  checkpoint/restart.c       |    4 +
>>>  checkpoint/rstr_file.c     |  202 ++++++++++++++++++++++++++++++++++++++++++++
>>>  include/linux/checkpoint.h |    1 +
>>>  4 files changed, 208 insertions(+), 1 deletions(-)
>>>  create mode 100644 checkpoint/rstr_file.c
>>>
>>> diff --git a/checkpoint/Makefile b/checkpoint/Makefile
>>> index 7496695..88bbc10 100644
>>> --- a/checkpoint/Makefile
>>> +++ b/checkpoint/Makefile
>>> @@ -3,4 +3,4 @@
>>>  #
>>>
>>>  obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o objhash.o \
>>> -		ckpt_mem.o rstr_mem.o ckpt_file.o
>>> +		ckpt_mem.o rstr_mem.o ckpt_file.o rstr_file.o
>>> diff --git a/checkpoint/restart.c b/checkpoint/restart.c
>>> index a0d5e60..956e274 100644
>>> --- a/checkpoint/restart.c
>>> +++ b/checkpoint/restart.c
>>> @@ -212,6 +212,10 @@ static int cr_read_task(struct cr_ctx *ctx)
>>>  	cr_debug("memory: ret %d\n", ret);
>>>  	if (ret < 0)
>>>  		goto out;
>>> +	ret = cr_read_files(ctx);
>>> +	cr_debug("files: ret %d\n", ret);
>>> +	if (ret < 0)
>>> +		goto out;
>>>  	ret = cr_read_thread(ctx);
>>>  	cr_debug("thread: ret %d\n", ret);
>>>  	if (ret < 0)
>>> diff --git a/checkpoint/rstr_file.c b/checkpoint/rstr_file.c
>>> new file mode 100644
>>> index 0000000..780c0fc
>>> --- /dev/null
>>> +++ b/checkpoint/rstr_file.c
>>> @@ -0,0 +1,202 @@
>>> +/*
>>> + *  Checkpoint file descriptors
>>> + *
>>> + *  Copyright (C) 2008 Oren Laadan
>>> + *
>>> + *  This file is subject to the terms and conditions of the GNU General Public
>>> + *  License.  See the file COPYING in the main directory of the Linux
>>> + *  distribution for more details.
>>> + */
>>> +
>>> +#include <linux/kernel.h>
>>> +#include <linux/sched.h>
>>> +#include <linux/fs.h>
>>> +#include <linux/file.h>
>>> +#include <linux/fdtable.h>
>>> +#include <linux/fsnotify.h>
>>> +#include <linux/syscalls.h>
>>> +#include <linux/checkpoint.h>
>>> +#include <linux/checkpoint_hdr.h>
>>> +
>>> +#include "checkpoint_file.h"
>>> +
>>> +static int cr_close_all_fds(struct files_struct *files)
>>> +{
>>> +	int *fdtable;
>>> +	int nfds;
>>> +
>>> +	nfds = cr_scan_fds(files, &fdtable);
>>> +	if (nfds < 0)
>>> +		return nfds;
>>> +	while (nfds--)
>>> +		sys_close(fdtable[nfds]);
>>> +	kfree(fdtable);
>>> +	return 0;
>>> +}
>>> +
>>> +/**
>>> + * cr_attach_file - attach a lonely file ptr to a file descriptor
>>> + * @file: lonely file pointer
>>> + */
>>> +static int cr_attach_file(struct file *file)
>>> +{
>>> +	int fd = get_unused_fd_flags(0);
>>> +
>>> +	if (fd >= 0) {
>>> +		fsnotify_open(file->f_path.dentry);
>>> +		fd_install(fd, file);
>>> +	}
>>> +	return fd;
>>> +}
>>> +
>>> +#define CR_SETFL_MASK (O_APPEND|O_NONBLOCK|O_NDELAY|FASYNC|O_DIRECT|O_NOATIME)
>>> +
>>> +/* cr_read_fd_data - restore the state of a given file pointer */
>>> +static int
>>> +cr_read_fd_data(struct cr_ctx *ctx, struct files_struct *files, int parent)
>>> +{
>>> +	struct cr_hdr_fd_data *hh = cr_hbuf_get(ctx, sizeof(*hh));
>>
>> You're leaking hh in a whole slew of error paths.
>
> No. (this was discussed earlier already).
>
> cr_hbuf_get() "allocates" space inside a dedicated buffer for headers
> in the checkpoint context (ctx->hbuf). It does not allocate new kernel
> memory. Instead, it returns the current position in that buffer
> ctx->hbuf[ctx->hpos], and advances ctx->hpos appropriately. On the
> other side, cr_hbuf_put() reverses that effect, reducing ctx->hpos
> accordingly.
>
> If an error occurs, the checkpoint (or restart) operation is aborted,
> and eventually the context (ctx) will be cleaned up; at that point the
> special purpose buffer will be freed.
>
> [...]
>
> Oren.

Yes I realize you're not doing a real allocation here and so, especially
if the whole thing is about to fail anyway, there may seem to be little
point in bothering to _put().  The thing is it's an unbalanced
operation, and the behind-the-scenes implementation may change at some
later point so IMO it's definately worth balancing these things now.

-serge
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