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    Subject[RFC v5][PATCH 8/8] Dump open file descriptors
    Date
    Dump the files_struct of a task with 'struct cr_hdr_files', followed by
    all open file descriptors. Since FDs can be shared, they are assigned an
    objref and registered in the object hash.

    For each open FD there is a 'struct cr_hdr_fd_ent' with the FD, its objref
    and its close-on-exec property. If the FD is to be saved (first time)
    then this is followed by a 'struct cr_hdr_fd_data' with the FD state.
    Then will come the next FD and so on.

    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/checkpoint.c | 4 +
    checkpoint/checkpoint_file.h | 17 +++
    checkpoint/ckpt_file.c | 221 ++++++++++++++++++++++++++++++++++++++++
    include/linux/checkpoint.h | 7 +-
    include/linux/checkpoint_hdr.h | 32 ++++++-
    6 files changed, 278 insertions(+), 5 deletions(-)
    create mode 100644 checkpoint/checkpoint_file.h
    create mode 100644 checkpoint/ckpt_file.c

    diff --git a/checkpoint/Makefile b/checkpoint/Makefile
    index 9843fb9..7496695 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_mem.o rstr_mem.o ckpt_file.o
    diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
    index d4c1b31..87420dc 100644
    --- a/checkpoint/checkpoint.c
    +++ b/checkpoint/checkpoint.c
    @@ -203,6 +203,10 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
    cr_debug("memory: ret %d\n", ret);
    if (ret < 0)
    goto out;
    + ret = cr_write_files(ctx, t);
    + cr_debug("files: ret %d\n", ret);
    + if (ret < 0)
    + goto out;
    ret = cr_write_thread(ctx, t);
    cr_debug("thread: ret %d\n", ret);
    if (ret < 0)
    diff --git a/checkpoint/checkpoint_file.h b/checkpoint/checkpoint_file.h
    new file mode 100644
    index 0000000..9dc3eba
    --- /dev/null
    +++ b/checkpoint/checkpoint_file.h
    @@ -0,0 +1,17 @@
    +#ifndef _CHECKPOINT_CKPT_FILE_H_
    +#define _CHECKPOINT_CKPT_FILE_H_
    +/*
    + * 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/fdtable.h>
    +
    +int cr_scan_fds(struct files_struct *files, int **fdtable);
    +
    +#endif /* _CHECKPOINT_CKPT_FILE_H_ */
    diff --git a/checkpoint/ckpt_file.c b/checkpoint/ckpt_file.c
    new file mode 100644
    index 0000000..bf049d1
    --- /dev/null
    +++ b/checkpoint/ckpt_file.c
    @@ -0,0 +1,221 @@
    +/*
    + * 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/file.h>
    +#include <linux/fdtable.h>
    +#include <linux/checkpoint.h>
    +#include <linux/checkpoint_hdr.h>
    +
    +#include "checkpoint_file.h"
    +
    +#define CR_DEFAULT_FDTABLE 256 /* an initial guess */
    +
    +/**
    + * cr_scan_fds - scan file table and construct array of open fds
    + * @files: files_struct pointer
    + * @fdtable: (output) array of open fds
    + *
    + * Returns the number of open fds found, and also the file table
    + * array via *fdtable. The caller should free the array.
    + */
    +int cr_scan_fds(struct files_struct *files, int **fdtable)
    +{
    + struct fdtable *fdt;
    + int *fds;
    + int i, n, tot;
    +
    + n = 0;
    + tot = CR_DEFAULT_FDTABLE;
    +
    + fds = kmalloc(tot * sizeof(*fds), GFP_KERNEL);
    + if (!fds)
    + return -ENOMEM;
    +
    + spin_lock(&files->file_lock);
    + fdt = files_fdtable(files);
    + for (i = 0; i < fdt->max_fds; i++) {
    + if (!fcheck_files(files, i))
    + continue;
    + if (n == tot) {
    + /*
    + * fcheck_files() is safe with drop/re-acquire
    + * of the lock, because it tests: fd < max_fds
    + */
    + spin_unlock(&files->file_lock);
    + tot *= 2;
    + if (tot < 0) { /* overflow ? */
    + kfree(fds);
    + return -EMFILE;
    + }
    + fds = krealloc(fds, tot * sizeof(*fds), GFP_KERNEL);
    + if (!fds)
    + return -ENOMEM;
    + spin_lock(&files->file_lock);
    + }
    + fds[n++] = i;
    + }
    + spin_unlock(&files->file_lock);
    +
    + *fdtable = fds;
    + return n;
    +}
    +
    +/* cr_write_fd_data - dump the state of a given file pointer */
    +static int cr_write_fd_data(struct cr_ctx *ctx, struct file *file, int parent)
    +{
    + struct cr_hdr h;
    + struct cr_hdr_fd_data *hh = cr_hbuf_get(ctx, sizeof(*hh));
    + struct dentry *dent = file->f_dentry;
    + struct inode *inode = dent->d_inode;
    + enum fd_type fd_type;
    + int ret;
    +
    + h.type = CR_HDR_FD_DATA;
    + h.len = sizeof(*hh);
    + h.parent = parent;
    +
    + hh->f_flags = file->f_flags;
    + hh->f_mode = file->f_mode;
    + hh->f_pos = file->f_pos;
    + hh->f_version = file->f_version;
    + /* FIX: need also file->uid, file->gid, file->f_owner, etc */
    +
    + switch (inode->i_mode & S_IFMT) {
    + case S_IFREG:
    + fd_type = CR_FD_FILE;
    + break;
    + case S_IFDIR:
    + fd_type = CR_FD_DIR;
    + break;
    + case S_IFLNK:
    + fd_type = CR_FD_LINK;
    + break;
    + default:
    + return -EBADF;
    + }
    +
    + /* FIX: check if the file/dir/link is unlinked */
    + hh->fd_type = fd_type;
    +
    + ret = cr_write_obj(ctx, &h, hh);
    + cr_hbuf_put(ctx, sizeof(*hh));
    + if (ret < 0)
    + return ret;
    +
    + return cr_write_fname(ctx, &file->f_path, ctx->vfsroot);
    +}
    +
    +/**
    + * cr_write_fd_ent - dump the state of a given file descriptor
    + * @ctx: checkpoint context
    + * @files: files_struct pointer
    + * @fd: file descriptor
    + *
    + * Saves the state of the file descriptor; looks up the actual file
    + * pointer in the hash table, and if found saves the matching objref,
    + * otherwise calls cr_write_fd_data to dump the file pointer too.
    + */
    +static int
    +cr_write_fd_ent(struct cr_ctx *ctx, struct files_struct *files, int fd)
    +{
    + struct cr_hdr h;
    + struct cr_hdr_fd_ent *hh = cr_hbuf_get(ctx, sizeof(*hh));
    + struct file *file = NULL;
    + struct fdtable *fdt;
    + int coe, objref, new, ret;
    +
    + rcu_read_lock();
    + fdt = files_fdtable(files);
    + file = fcheck_files(files, fd);
    + if (file) {
    + coe = FD_ISSET(fd, fdt->close_on_exec);
    + get_file(file);
    + }
    + rcu_read_unlock();
    +
    + /* sanity check (although this shouldn't happen) */
    + if (!file)
    + return -EBADF;
    +
    + new = cr_obj_add_ptr(ctx, (void *) file, &objref, CR_OBJ_FILE, 0);
    + cr_debug("fd %d objref %d file %p c-o-e %d)\n", fd, objref, file, coe);
    +
    + if (new < 0) {
    + ret = new;
    + goto out;
    + }
    +
    + h.type = CR_HDR_FD_ENT;
    + h.len = sizeof(*hh);
    + h.parent = 0;
    +
    + hh->objref = objref;
    + hh->fd = fd;
    + hh->close_on_exec = coe;
    +
    + ret = cr_write_obj(ctx, &h, hh);
    + cr_hbuf_put(ctx, sizeof(*hh));
    + if (ret < 0)
    + goto out;
    +
    + /* new==1 if-and-only-if file was newly added to hash */
    + if (new)
    + ret = cr_write_fd_data(ctx, file, objref);
    +
    +out:
    + fput(file);
    + return ret;
    +}
    +
    +int cr_write_files(struct cr_ctx *ctx, struct task_struct *t)
    +{
    + struct cr_hdr h;
    + struct cr_hdr_files *hh = cr_hbuf_get(ctx, sizeof(*hh));
    + struct files_struct *files;
    + int *fdtable;
    + int nfds, n, ret;
    +
    + h.type = CR_HDR_FILES;
    + h.len = sizeof(*hh);
    + h.parent = task_pid_vnr(t);
    +
    + files = get_files_struct(t);
    +
    + hh->objref = 0; /* will be meaningful with multiple processes */
    +
    + nfds = cr_scan_fds(files, &fdtable);
    + if (nfds < 0) {
    + ret = nfds;
    + goto out;
    + }
    +
    + hh->nfds = nfds;
    +
    + ret = cr_write_obj(ctx, &h, hh);
    + cr_hbuf_put(ctx, sizeof(*hh));
    + if (ret < 0)
    + goto clean;
    +
    + cr_debug("nfds %d\n", nfds);
    + for (n = 0; n < nfds; n++) {
    + ret = cr_write_fd_ent(ctx, files, fdtable[n]);
    + if (ret < 0)
    + break;
    + }
    +
    + clean:
    + kfree(fdtable);
    + out:
    + put_files_struct(files);
    +
    + return ret;
    +}
    diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
    index 9990bb1..a202c54 100644
    --- a/include/linux/checkpoint.h
    +++ b/include/linux/checkpoint.h
    @@ -13,7 +13,7 @@
    #include <linux/path.h>
    #include <linux/fs.h>

    -#define CR_VERSION 1
    +#define CR_VERSION 2

    struct cr_ctx {
    pid_t pid; /* container identifier */
    @@ -83,11 +83,12 @@ extern int cr_read_fname(struct cr_ctx *ctx, void *fname, int n);
    extern struct file *cr_read_open_fname(struct cr_ctx *ctx,
    int flags, int mode);

    +extern int do_checkpoint(struct cr_ctx *ctx);
    extern int cr_write_mm(struct cr_ctx *ctx, struct task_struct *t);
    -extern int cr_read_mm(struct cr_ctx *ctx);
    +extern int cr_write_files(struct cr_ctx *ctx, struct task_struct *t);

    -extern int do_checkpoint(struct cr_ctx *ctx);
    extern int do_restart(struct cr_ctx *ctx);
    +extern int cr_read_mm(struct cr_ctx *ctx);

    #define cr_debug(fmt, args...) \
    pr_debug("[CR:%s] " fmt, __func__, ## args)
    diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
    index 2b110f1..cbb920f 100644
    --- a/include/linux/checkpoint_hdr.h
    +++ b/include/linux/checkpoint_hdr.h
    @@ -17,7 +17,7 @@
    /*
    * To maintain compatibility between 32-bit and 64-bit architecture flavors,
    * keep data 64-bit aligned: use padding for structure members, and use
    - * __attribute__ ((aligned (8))) for the entire structure.
    + * __attribute__((aligned(8))) for the entire structure.
    */

    /* records: generic header */
    @@ -43,6 +43,10 @@ enum {
    CR_HDR_PGARR,
    CR_HDR_MM_CONTEXT,

    + CR_HDR_FILES = 301,
    + CR_HDR_FD_ENT,
    + CR_HDR_FD_DATA,
    +
    CR_HDR_TAIL = 5001
    };

    @@ -105,4 +109,30 @@ struct cr_hdr_pgarr {
    __u64 nr_pages; /* number of pages to saved */
    } __attribute__((aligned(8)));

    +struct cr_hdr_files {
    + __u32 objref; /* identifier for shared objects */
    + __u32 nfds;
    +} __attribute__((aligned(8)));
    +
    +struct cr_hdr_fd_ent {
    + __u32 objref; /* identifier for shared objects */
    + __s32 fd;
    + __u32 close_on_exec;
    +} __attribute__((aligned(8)));
    +
    +/* fd types */
    +enum fd_type {
    + CR_FD_FILE = 1,
    + CR_FD_DIR,
    + CR_FD_LINK
    +};
    +
    +struct cr_hdr_fd_data {
    + __u16 fd_type;
    + __u16 f_mode;
    + __u32 f_flags;
    + __u64 f_pos;
    + __u64 f_version;
    +} __attribute__((aligned(8)));
    +
    #endif /* _CHECKPOINT_CKPT_HDR_H_ */
    --
    1.5.4.3


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