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

Serge E. Hallyn
2008-09-17T04:57:14Z

Quoting Oren Laadan (orenl@cs.columbia.edu):
>
>
> Serge E. Hallyn wrote:
>> Quoting Oren Laadan (orenl@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@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