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    SubjectRe: [RFC v4][PATCH 8/9] File descriprtors (dump)
    On Tue, Sep 9, 2008 at 4:42 PM, Oren Laadan <orenl@cs.columbia.edu> wrote:
    > 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/ckpt_file.c | 221 ++++++++++++++++++++++++++++++++++++++++++++++
    > checkpoint/ckpt_file.h | 17 ++++
    > include/linux/ckpt.h | 7 +-
    > include/linux/ckpt_hdr.h | 34 +++++++-
    > 6 files changed, 280 insertions(+), 5 deletions(-)
    > create mode 100644 checkpoint/ckpt_file.c
    > create mode 100644 checkpoint/ckpt_file.h
    >
    > 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 4dae775..aebbf22 100644
    > --- a/checkpoint/checkpoint.c
    > +++ b/checkpoint/checkpoint.c
    > @@ -217,6 +217,10 @@ 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/ckpt_file.c b/checkpoint/ckpt_file.c
    > new file mode 100644
    > index 0000000..ca58b28
    > --- /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/ckpt.h>
    > +#include <linux/ckpt_hdr.h>
    > +
    > +#include "ckpt_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
    > + * @return: the number of open fds found
    > + *
    > + * Allocates the file descriptors array (*fdtable), caller should free
    > + */
    > +int cr_scan_fds(struct files_struct *files, int **fdtable)
    > +{
    > + struct fdtable *fdt;
    > + int *fdlist;
    > + int i, n, max;
    > +
    > + n = 0;
    > + max = CR_DEFAULT_FDTABLE;

    max is read-only variable so that you don't need to declare local variable.
    You can use macro.

    > + fdlist = kmalloc(max * sizeof(*fdlist), GFP_KERNEL);
    > + if (!fdlist)
    > + 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 == max) {
    > + /* fcheck_files() is safe with drop/re-acquire
    > + * of the lock, as it tests: fd < max_fds */
    > + spin_unlock(&files->file_lock);
    > + max *= 2;
    > + if (max < 0) { /* overflow ? */
    > + n = -EMFILE;
    > + goto out;
    > + }
    > + fdlist = krealloc(fdlist, max, GFP_KERNEL);
    > + if (!fdlist) {
    > + n = -ENOMEM;
    > + goto out;
    > + }
    > + spin_lock(&files->file_lock);
    > + }
    > + fdlist[n++] = i;
    > + }
    > + spin_unlock(&files->file_lock);
    > +
    > + *fdtable = fdlist;
    > + out:
    > + 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_uid = file->f_uid;
    > + hh->f_gid = file->f_gid;
    > + hh->f_version = file->f_version;
    > + /* FIX: need also file->f_owner */
    > +
    > + 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
    > + *
    > + * Save the state of the file descriptor; look up the actual file pointer
    > + * in the hash table, and if found save the matching objref, otherwise call
    > + * 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)
    > + return new;
    > +
    > + 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)
    > + return ret;
    > +
    > + /* new==1 if-and-only-if file was newly added to hash */
    > + if (new)
    > + ret = cr_write_fd_data(ctx, file, objref);
    > +
    > + 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, n);

    I think your intention is not 'n' but 'fdtable[n]' in argument.

    > + if (ret < 0)
    > + break;
    > + }
    > +
    > + clean:
    > + kfree(fdtable);
    > + out:
    > + put_files_struct(files);
    > +
    > + return ret;
    > +}
    > diff --git a/checkpoint/ckpt_file.h b/checkpoint/ckpt_file.h
    > new file mode 100644
    > index 0000000..9dc3eba
    > --- /dev/null
    > +++ b/checkpoint/ckpt_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/include/linux/ckpt.h b/include/linux/ckpt.h
    > index d73f79e..ad46baf 100644
    > --- a/include/linux/ckpt.h
    > +++ b/include/linux/ckpt.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 */
    > @@ -80,11 +80,12 @@ int cr_read_string(struct cr_ctx *ctx, void *str, int len);
    > int cr_read_fname(struct cr_ctx *ctx, void *fname, int n);
    > struct file *cr_read_open_fname(struct cr_ctx *ctx, int flags, int mode);
    >
    > +int do_checkpoint(struct cr_ctx *ctx);
    > int cr_write_mm(struct cr_ctx *ctx, struct task_struct *t);
    > -int cr_read_mm(struct cr_ctx *ctx);
    > +int cr_write_files(struct cr_ctx *ctx, struct task_struct *t);
    >
    > -int do_checkpoint(struct cr_ctx *ctx);
    > int do_restart(struct cr_ctx *ctx);
    > +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/ckpt_hdr.h b/include/linux/ckpt_hdr.h
    > index f064cbb..f868dce 100644
    > --- a/include/linux/ckpt_hdr.h
    > +++ b/include/linux/ckpt_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 */
    > @@ -42,6 +42,10 @@ enum {
    > CR_HDR_VMA,
    > CR_HDR_MM_CONTEXT,
    >
    > + CR_HDR_FILES = 301,
    > + CR_HDR_FD_ENT,
    > + CR_HDR_FD_DATA,
    > +
    > CR_HDR_TAIL = 5001
    > };
    >
    > @@ -112,4 +116,32 @@ struct cr_hdr_vma {
    >
    > } __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;
    > + __u32 f_uid;
    > + __u32 f_gid;
    > + __u64 f_pos;
    > + __u64 f_version;
    > +} __attribute__((aligned(8)));
    > +
    > #endif /* _CHECKPOINT_CKPT_HDR_H_ */
    > --
    > 1.5.4.3
    >
    > --
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    --
    Kinds regards,
    MinChan Kim


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