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    Subject[RFC v16][PATCH 10/43] c/r: restore open file descriptors
    Date
    For each fd read 'struct ckpt_hdr_file_desc' and lookup objref in the
    hash table; If not found in the hash table, (first occurence), read in
    'struct ckpt_hdr_file', create a new file and register in the hash.
    Otherwise attach the file pointer from the hash as an FD.

    Changelog[v16]:
    - Reorder patch (move earlier in series)
    - Handle shared files_struct objects

    Changelog[v14]:
    - Introduce a per file-type restore() callback
    - Revert change to pr_debug(), back to ckpt_debug()
    - Rename: restore_files() => restore_fd_table()
    - Rename: ckpt_read_fd_data() => restore_file()
    - Check whether calls to ckpt_hbuf_get() fail
    - Discard field 'hh->parent'

    Changelog[v12]:
    - Replace obsolete ckpt_debug() with pr_debug()

    Changelog[v6]:
    - Balance all calls to ckpt_hbuf_get() with matching ckpt_hbuf_put()
    (even though it's not really needed)

    Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
    ---
    checkpoint/files.c | 285 ++++++++++++++++++++++++++++++++++++++++++++
    checkpoint/objhash.c | 2 +
    checkpoint/process.c | 20 +++
    checkpoint/restart.c | 9 ++
    include/linux/checkpoint.h | 5 +
    5 files changed, 321 insertions(+), 0 deletions(-)

    diff --git a/checkpoint/files.c b/checkpoint/files.c
    index d10dfb6..d7583d3 100644
    --- a/checkpoint/files.c
    +++ b/checkpoint/files.c
    @@ -16,6 +16,8 @@
    #include <linux/sched.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>

    @@ -309,3 +311,286 @@ int checkpoint_obj_file_table(struct ckpt_ctx *ctx, struct task_struct *t)

    return objref;
    }
    +
    +/**************************************************************************
    + * Restart
    + */
    +
    +/**
    + * read_open_fname - read a file name and open a file
    + * @ctx: checkpoint context
    + * @flags: file flags
    + * @mode: file mode
    + */
    +static struct file *read_open_fname(struct ckpt_ctx *ctx, int flags, int mode)
    +{
    + struct ckpt_hdr *h;
    + struct file *file;
    + char *fname;
    +
    + h = ckpt_read_buf_type(ctx, PATH_MAX, CKPT_HDR_FILE_NAME);
    + if (IS_ERR(h))
    + return (struct file *) h;
    + fname = (char *) (h + 1);
    + ckpt_debug("fname '%s' flags %#x mode %#x\n", fname, flags, mode);
    +
    + file = filp_open(fname, flags, mode);
    + ckpt_hdr_put(ctx, h);
    + return file;
    +}
    +
    +static int close_all_fds(struct files_struct *files)
    +{
    + int *fdtable;
    + int nfds;
    +
    + nfds = scan_fds(files, &fdtable);
    + if (nfds < 0)
    + return nfds;
    + while (nfds--)
    + sys_close(fdtable[nfds]);
    + kfree(fdtable);
    + return 0;
    +}
    +
    +/**
    + * attach_file - attach a lonely file ptr to a file descriptor
    + * @file: lonely file pointer
    + */
    +static int attach_file(struct file *file)
    +{
    + int fd = get_unused_fd_flags(0);
    +
    + if (fd >= 0) {
    + get_file(file);
    + fsnotify_open(file->f_path.dentry);
    + fd_install(fd, file);
    + }
    + return fd;
    +}
    +
    +#define CKPT_SETFL_MASK \
    + (O_APPEND | O_NONBLOCK | O_NDELAY | FASYNC | O_DIRECT | O_NOATIME)
    +
    +int restore_file_common(struct ckpt_ctx *ctx, struct file *file,
    + struct ckpt_hdr_file *h)
    +{
    + int ret;
    +
    + /* FIX: need to restore uid, gid, owner etc */
    +
    + /* safe to set 1st arg (fd) to 0, as command is F_SETFL */
    + ret = vfs_fcntl(0, F_SETFL, h->f_flags & CKPT_SETFL_MASK, file);
    + if (ret < 0)
    + goto out;
    +
    + ret = vfs_llseek(file, h->f_pos, SEEK_SET);
    + if (ret == -ESPIPE) /* ignore error on non-seekable files */
    + ret = 0;
    + out:
    + return ret;
    +}
    +
    +static struct file *generic_file_restore(struct ckpt_ctx *ctx,
    + struct ckpt_hdr_file *ptr)
    +{
    + struct file *file;
    + int ret;
    +
    + if (ptr->h.type != CKPT_HDR_FILE ||
    + ptr->h.len != sizeof(*ptr) || ptr->f_type != CKPT_FILE_GENERIC)
    + return ERR_PTR(-EINVAL);
    +
    + file = read_open_fname(ctx, ptr->f_flags, ptr->f_mode);
    + if (IS_ERR(file))
    + return file;
    +
    + ret = restore_file_common(ctx, file, ptr);
    + if (ret < 0) {
    + fput(file);
    + file = ERR_PTR(ret);
    + }
    + return file;
    +}
    +
    +struct restore_file_ops {
    + char *file_name;
    + enum file_type file_type;
    + struct file * (*restore) (struct ckpt_ctx *ctx,
    + struct ckpt_hdr_file *ptr);
    +};
    +
    +static struct restore_file_ops restore_file_ops[] = {
    + /* ignored file */
    + {
    + .file_name = "IGNORE",
    + .file_type = CKPT_FILE_IGNORE,
    + .restore = NULL,
    + },
    + /* regular file/directory */
    + {
    + .file_name = "GENERIC",
    + .file_type = CKPT_FILE_GENERIC,
    + .restore = generic_file_restore,
    + },
    +};
    +
    +static struct file *do_restore_file(struct ckpt_ctx *ctx)
    +{
    + struct restore_file_ops *ops;
    + struct ckpt_hdr_file *h;
    + struct file *file = ERR_PTR(-EINVAL);
    +
    + /*
    + * All 'struct ckpt_hdr_file_...' begin with ckpt_hdr_file,
    + * but the actual object depends on the file type. The length
    + * should never be more than page.
    + */
    + h = ckpt_read_buf_type(ctx, PAGE_SIZE, CKPT_HDR_FILE);
    + if (IS_ERR(h))
    + return (struct file *) h;
    + ckpt_debug("flags %#x mode %#x type %d\n",
    + h->f_flags, h->f_mode, h->f_type);
    +
    + if (h->f_type >= CKPT_FILE_MAX)
    + goto out;
    +
    + ops = &restore_file_ops[h->f_type];
    + BUG_ON(ops->file_type != h->f_type);
    +
    + if (ops->restore)
    + file = ops->restore(ctx, h);
    + out:
    + ckpt_hdr_put(ctx, h);
    + return file;
    +}
    +
    +/* restore callback for file pointer */
    +void *restore_file(struct ckpt_ctx *ctx)
    +{
    + return (void *) do_restore_file(ctx);
    +}
    +
    +/**
    + * ckpt_read_file_desc - restore the state of a given file descriptor
    + * @ctx: checkpoint context
    + *
    + * Restores the state of a file descriptor; looks up the objref (in the
    + * header) in the hash table, and if found picks the matching file and
    + * use it; otherwise calls restore_file to restore the file too.
    + */
    +static int restore_file_desc(struct ckpt_ctx *ctx)
    +{
    + struct ckpt_hdr_file_desc *h;
    + struct file *file;
    + int newfd, ret;
    +
    + h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_FILE_DESC);
    + if (IS_ERR(h))
    + return PTR_ERR(h);
    + ckpt_debug("ref %d fd %d c.o.e %d\n",
    + h->fd_objref, h->fd_descriptor, h->fd_close_on_exec);
    +
    + ret = -EINVAL;
    + if (h->fd_objref <= 0 || h->fd_descriptor < 0)
    + goto out;
    +
    + file = ckpt_obj_fetch(ctx, h->fd_objref, CKPT_OBJ_FILE);
    + if (IS_ERR(file)) {
    + ret = PTR_ERR(file);
    + goto out;
    + }
    +
    + newfd = attach_file(file);
    + if (newfd < 0) {
    + ret = newfd;
    + goto out;
    + }
    +
    + ckpt_debug("newfd got %d wanted %d\n", newfd, h->fd_descriptor);
    +
    + /* reposition if newfd isn't desired fd */
    + if (newfd != h->fd_descriptor) {
    + ret = sys_dup2(newfd, h->fd_descriptor);
    + if (ret < 0)
    + goto out;
    + sys_close(newfd);
    + }
    +
    + if (h->fd_close_on_exec)
    + set_close_on_exec(h->fd_descriptor, 1);
    +
    + ret = 0;
    + out:
    + ckpt_hdr_put(ctx, h);
    + return ret;
    +}
    +
    +/* restore callback for file table */
    +static struct files_struct *do_restore_file_table(struct ckpt_ctx *ctx)
    +{
    + struct ckpt_hdr_file_table *h;
    + struct files_struct *files;
    + int i, ret;
    +
    + h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_FILE_TABLE);
    + if (IS_ERR(h))
    + return (struct files_struct *) h;
    +
    + ckpt_debug("nfds %d\n", h->fdt_nfds);
    +
    + ret = -EMFILE;
    + if (h->fdt_nfds < 0 || h->fdt_nfds > sysctl_nr_open)
    + goto out;
    +
    + /*
    + * We assume that restarting tasks, as created in user-space,
    + * have distinct files_struct objects each. If not, we need to
    + * call dup_fd() to make sure we don't overwrite an already
    + * restored one.
    + */
    +
    + /* point of no return -- close all file descriptors */
    + ret = close_all_fds(current->files);
    + if (ret < 0)
    + goto out;
    +
    + for (i = 0; i < h->fdt_nfds; i++) {
    + ret = restore_file_desc(ctx);
    + if (ret < 0)
    + break;
    + }
    + out:
    + ckpt_hdr_put(ctx, h);
    + if (!ret) {
    + files = current->files;
    + atomic_inc(&files->count);
    + } else {
    + files = ERR_PTR(ret);
    + }
    + return files;
    +}
    +
    +void *restore_file_table(struct ckpt_ctx *ctx)
    +{
    + return (void *) do_restore_file_table(ctx);
    +}
    +
    +int restore_obj_file_table(struct ckpt_ctx *ctx, int files_objref)
    +{
    + struct files_struct *files;
    +
    + files = ckpt_obj_fetch(ctx, files_objref, CKPT_OBJ_FILE_TABLE);
    + if (IS_ERR(files))
    + return PTR_ERR(files);
    +
    + if (files != current->files) {
    + task_lock(current);
    + put_files_struct(current->files);
    + current->files = files;
    + task_unlock(current);
    + atomic_inc(&files->count);
    + }
    +
    + return 0;
    +}
    diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
    index ea15958..f5c9f7c 100644
    --- a/checkpoint/objhash.c
    +++ b/checkpoint/objhash.c
    @@ -92,6 +92,7 @@ static struct ckpt_obj_ops ckpt_obj_ops[] = {
    .ref_drop = obj_file_table_drop,
    .ref_grab = obj_file_table_grab,
    .checkpoint = checkpoint_file_table,
    + .restore = restore_file_table,
    },
    /* file object */
    {
    @@ -100,6 +101,7 @@ static struct ckpt_obj_ops ckpt_obj_ops[] = {
    .ref_drop = obj_file_drop,
    .ref_grab = obj_file_grab,
    .checkpoint = checkpoint_file,
    + .restore = restore_file,
    },
    };

    diff --git a/checkpoint/process.c b/checkpoint/process.c
    index 4c922b6..5fd1573 100644
    --- a/checkpoint/process.c
    +++ b/checkpoint/process.c
    @@ -121,6 +121,22 @@ static int restore_task_struct(struct ckpt_ctx *ctx)
    return ret;
    }

    +static int restore_task_objs(struct ckpt_ctx *ctx)
    +{
    + struct ckpt_hdr_task_objs *h;
    + int ret;
    +
    + h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TASK_OBJS);
    + if (IS_ERR(h))
    + return PTR_ERR(h);
    +
    + ret = restore_obj_file_table(ctx, h->files_objref);
    + ckpt_debug("file_table: ret %d (%p)\n", ret, current->files);
    +
    + ckpt_hdr_put(ctx, h);
    + return ret;
    +}
    +
    /* read the entire state of the current task */
    int restore_task(struct ckpt_ctx *ctx)
    {
    @@ -130,6 +146,10 @@ int restore_task(struct ckpt_ctx *ctx)
    ckpt_debug("task %d\n", ret);
    if (ret < 0)
    goto out;
    + ret = restore_task_objs(ctx);
    + ckpt_debug("shared %d\n", ret);
    + if (ret < 0)
    + goto out;
    ret = restore_thread(ctx);
    ckpt_debug("thread %d\n", ret);
    if (ret < 0)
    diff --git a/checkpoint/restart.c b/checkpoint/restart.c
    index ce52e30..d3d6c5e 100644
    --- a/checkpoint/restart.c
    +++ b/checkpoint/restart.c
    @@ -351,10 +351,19 @@ static int restore_read_tail(struct ckpt_ctx *ctx)
    return ret;
    }

    +/* setup restart-specific parts of ctx */
    +static int init_restart_ctx(struct ckpt_ctx *ctx)
    +{
    + return 0;
    +}
    +
    int do_restart(struct ckpt_ctx *ctx, pid_t pid)
    {
    int ret;

    + ret = init_restart_ctx(ctx);
    + if (ret < 0)
    + return ret;
    ret = restore_read_header(ctx);
    if (ret < 0)
    return ret;
    diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
    index d170988..bb14a66 100644
    --- a/include/linux/checkpoint.h
    +++ b/include/linux/checkpoint.h
    @@ -70,13 +70,18 @@ extern int restore_cpu(struct ckpt_ctx *ctx);
    /* file table */
    extern int checkpoint_obj_file_table(struct ckpt_ctx *ctx,
    struct task_struct *t);
    +extern int restore_obj_file_table(struct ckpt_ctx *ctx, int files_objref);
    extern int checkpoint_file_table(struct ckpt_ctx *ctx, void *ptr);
    +extern void *restore_file_table(struct ckpt_ctx *ctx);

    /* files */
    extern int checkpoint_file(struct ckpt_ctx *ctx, void *ptr);
    +extern void *restore_file(struct ckpt_ctx *ctx);

    extern int checkpoint_file_common(struct ckpt_ctx *ctx, struct file *file,
    struct ckpt_hdr_file *h);
    +extern int restore_file_common(struct ckpt_ctx *ctx, struct file *file,
    + struct ckpt_hdr_file *h);


    /* debugging flags */
    --
    1.6.0.4


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