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


    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.




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