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Subject[RFC v16][PATCH 09/43] c/r: dump open file descriptors
Date
Dump the file table with 'struct ckpt_hdr_file_table, followed by all
open file descriptors. Because the 'struct file' corresponding to an
fd can be shared, they are assigned an objref and registered in the
object hash. A reference to the 'file *' is kept for as long as it
lives in the hash (the hash is only cleaned up at the end of the
checkpoint).

Also provide generic_checkpoint_file() and generic_restore_file()
which is good for normal files and directories. It does not support
yet unlinked files or directories.

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

Changelog[v14]:
- File objects are dumped/restored prior to the first reference
- Introduce a per file-type restore() callback
- Use struct file_operations->checkpoint()
- Put code for generic file descriptors in a separate function
- Use one CKPT_FILE_GENERIC for both regular files and dirs
- Revert change to pr_debug(), back to ckpt_debug()
- Use only unsigned fields in checkpoint headers
- Rename: ckpt_write_files() => checkpoint_fd_table()
- Rename: ckpt_write_fd_data() => checkpoint_file()
- Discard field 'h->parent'

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

Changelog[v11]:
- Discard handling of opened symlinks (there is no such thing)
- ckpt_scan_fds() retries from scratch if hits size limits

Changelog[v9]:
- Fix a couple of leaks in ckpt_write_files()
- Drop useless kfree from ckpt_scan_fds()

Changelog[v8]:
- initialize 'coe' to workaround gcc false warning

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/Makefile | 3 +-
checkpoint/checkpoint.c | 25 +++
checkpoint/files.c | 311 ++++++++++++++++++++++++++++++++++++++
checkpoint/objhash.c | 40 +++++
checkpoint/process.c | 28 ++++
checkpoint/sys.c | 1 +
include/linux/checkpoint.h | 14 ++-
include/linux/checkpoint_hdr.h | 49 ++++++
include/linux/checkpoint_types.h | 8 +
include/linux/fs.h | 4 +
10 files changed, 481 insertions(+), 2 deletions(-)

diff --git a/checkpoint/Makefile b/checkpoint/Makefile
index 5aa6a75..1d0c058 100644
--- a/checkpoint/Makefile
+++ b/checkpoint/Makefile
@@ -7,4 +7,5 @@ obj-$(CONFIG_CHECKPOINT) += \
objhash.o \
checkpoint.o \
restart.o \
- process.o
+ process.o \
+ files.o
diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index 409c78b..a346b7e 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -15,6 +15,7 @@
#include <linux/time.h>
#include <linux/fs.h>
#include <linux/file.h>
+#include <linux/fs_struct.h>
#include <linux/dcache.h>
#include <linux/mount.h>
#include <linux/utsname.h>
@@ -244,10 +245,34 @@ static int checkpoint_write_tail(struct ckpt_ctx *ctx)
return ret;
}

+/* setup checkpoint-specific parts of ctx */
+static int init_checkpoint_ctx(struct ckpt_ctx *ctx, pid_t pid)
+{
+ struct fs_struct *fs;
+
+ ctx->root_pid = pid;
+
+ /*
+ * assume checkpointer is in container's root vfs
+ * FIXME: this works for now, but will change with real containers
+ */
+
+ fs = current->fs;
+ read_lock(&fs->lock);
+ ctx->fs_mnt = fs->root;
+ path_get(&ctx->fs_mnt);
+ read_unlock(&fs->lock);
+
+ return 0;
+}
+
int do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
{
int ret;

+ ret = init_checkpoint_ctx(ctx, pid);
+ if (ret < 0)
+ goto out;
ret = checkpoint_write_header(ctx);
if (ret < 0)
goto out;
diff --git a/checkpoint/files.c b/checkpoint/files.c
new file mode 100644
index 0000000..d10dfb6
--- /dev/null
+++ b/checkpoint/files.c
@@ -0,0 +1,311 @@
+/*
+ * Checkpoint file descriptors
+ *
+ * Copyright (C) 2008-2009 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.
+ */
+
+/* default debug level for output */
+#define CKPT_DFLAG CKPT_DFILE
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/checkpoint.h>
+#include <linux/checkpoint_hdr.h>
+
+
+/**************************************************************************
+ * Checkpoint
+ */
+
+/**
+ * fill_fname - return pathname of a given file
+ * @path: path name
+ * @root: relative root
+ * @buf: buffer for pathname
+ * @len: buffer length (in) and pathname length (out)
+ */
+static char *fill_fname(struct path *path, struct path *root,
+ char *buf, int *len)
+{
+ struct path tmp = *root;
+ char *fname;
+
+ BUG_ON(!buf);
+ spin_lock(&dcache_lock);
+ fname = __d_path(path, &tmp, buf, *len);
+ spin_unlock(&dcache_lock);
+ if (IS_ERR(fname))
+ return fname;
+ *len = (buf + (*len) - fname);
+ /*
+ * FIX: if __d_path() changed these, it must have stepped out of
+ * init's namespace. Since currently we require a unified namespace
+ * within the container: simply fail.
+ */
+ if (tmp.mnt != root->mnt || tmp.dentry != root->dentry)
+ fname = ERR_PTR(-EBADF);
+
+ return fname;
+}
+
+/**
+ * dump_fname - write a file name
+ * @ctx: checkpoint context
+ * @path: path name
+ * @root: relative root
+ */
+static int dump_fname(struct ckpt_ctx *ctx,
+ struct path *path, struct path *root)
+{
+ char *buf, *fname;
+ int ret, flen;
+
+ /*
+ * FIXME: we can optimize and save memory (and storage) if we
+ * share strings (through objhash) and reference them instead
+ */
+
+ flen = PATH_MAX;
+ buf = kmalloc(flen, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ fname = fill_fname(path, root, buf, &flen);
+ if (!IS_ERR(fname))
+ ret = ckpt_write_obj_type(ctx, fname, flen,
+ CKPT_HDR_FILE_NAME);
+ else
+ ret = PTR_ERR(fname);
+
+ kfree(buf);
+ return ret;
+}
+
+#define CKPT_DEFAULT_FDTABLE 256 /* an initial guess */
+
+/**
+ * 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.
+ *
+ * The caller must validate the file descriptors collected in the
+ * array before using them, e.g. by using fcheck_files(), in case
+ * the task's fdtable changes in the meantime.
+ */
+static int scan_fds(struct files_struct *files, int **fdtable)
+{
+ struct fdtable *fdt;
+ int *fds = NULL;
+ int i = 0, n = 0;
+ int tot = CKPT_DEFAULT_FDTABLE;
+
+ /*
+ * We assume that all tasks possibly sharing the file table are
+ * frozen (or we are a single process and we checkpoint ourselves).
+ * Therefore, we can safely proceed after krealloc() from where we
+ * left off. Otherwise the file table may be modified by another
+ * task after we scan it. The behavior is this case is undefined,
+ * and either checkpoint or restart will likely fail.
+ */
+ retry:
+ fds = krealloc(fds, tot * sizeof(*fds), GFP_KERNEL);
+ if (!fds)
+ return -ENOMEM;
+
+ spin_lock(&files->file_lock);
+ rcu_read_lock();
+ fdt = files_fdtable(files);
+ for (/**/; i < fdt->max_fds; i++) {
+ if (!fcheck_files(files, i))
+ continue;
+ if (n == tot) {
+ spin_unlock(&files->file_lock);
+ rcu_read_unlock();
+ tot *= 2; /* won't overflow: kmalloc will fail */
+ goto retry;
+ }
+ fds[n++] = i;
+ }
+ rcu_read_unlock();
+ spin_unlock(&files->file_lock);
+
+ *fdtable = fds;
+ return n;
+}
+
+int checkpoint_file_common(struct ckpt_ctx *ctx, struct file *file,
+ struct ckpt_hdr_file *h)
+{
+ h->f_flags = file->f_flags;
+ h->f_mode = file->f_mode;
+ h->f_pos = file->f_pos;
+ h->f_version = file->f_version;
+
+ /* FIX: need also file->uid, file->gid, file->f_owner, etc */
+
+ return 0;
+}
+
+int generic_file_checkpoint(struct ckpt_ctx *ctx, struct file *file)
+{
+ struct ckpt_hdr_file_generic *h;
+ int ret;
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_FILE);
+ if (!h)
+ return -ENOMEM;
+
+ /*
+ * FIXME: when we'll add support for unlinked files/dirs, we'll
+ * need to distinguish between unlinked filed and unlinked dirs.
+ */
+ h->common.f_type = CKPT_FILE_GENERIC;
+
+ ret = checkpoint_file_common(ctx, file, &h->common);
+ if (ret < 0)
+ goto out;
+ ret = ckpt_write_obj(ctx, &h->common.h);
+ if (ret < 0)
+ goto out;
+ ret = dump_fname(ctx, &file->f_path, &ctx->fs_mnt);
+ out:
+ ckpt_hdr_put(ctx, h);
+ return ret;
+}
+EXPORT_SYMBOL(generic_file_checkpoint);
+
+/* checkpoint callback for file pointer */
+int checkpoint_file(struct ckpt_ctx *ctx, void *ptr)
+{
+ struct file *file = (struct file *) ptr;
+
+ if (!file->f_op->checkpoint)
+ return -EBADF;
+ return file->f_op->checkpoint(ctx, file);
+}
+
+/**
+ * ckpt_write_file_desc - 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 ckpt_write_file to dump the file pointer too.
+ */
+static int checkpoint_file_desc(struct ckpt_ctx *ctx,
+ struct files_struct *files, int fd)
+{
+ struct ckpt_hdr_file_desc *h;
+ struct file *file = NULL;
+ struct fdtable *fdt;
+ int objref, ret;
+ int coe = 0; /* avoid gcc warning */
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_FILE_DESC);
+ if (!h)
+ return -ENOMEM;
+
+ 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) */
+ ret = -EBADF;
+ if (!file)
+ goto out;
+
+ /*
+ * if seen first time, this will add 'file' to the objhash, keep
+ * a reference to it, dump its state while at it.
+ */
+ objref = checkpoint_obj(ctx, file, CKPT_OBJ_FILE);
+ ckpt_debug("fd %d objref %d file %p coe %d)\n", fd, objref, file, coe);
+ if (objref < 0) {
+ ret = objref;
+ goto out;
+ }
+
+ h->fd_objref = objref;
+ h->fd_descriptor = fd;
+ h->fd_close_on_exec = coe;
+
+ ret = ckpt_write_obj(ctx, &h->h);
+out:
+ ckpt_hdr_put(ctx, h);
+ if (file)
+ fput(file);
+ return ret;
+}
+
+static int do_checkpoint_file_table(struct ckpt_ctx *ctx,
+ struct files_struct *files)
+{
+ struct ckpt_hdr_file_table *h;
+ int *fdtable = NULL;
+ int nfds, n, ret;
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_FILE_TABLE);
+ if (!h)
+ return -ENOMEM;
+
+ nfds = scan_fds(files, &fdtable);
+ if (nfds < 0) {
+ ret = nfds;
+ goto out;
+ }
+
+ h->fdt_nfds = nfds;
+
+ ret = ckpt_write_obj(ctx, &h->h);
+ ckpt_hdr_put(ctx, h);
+ if (ret < 0)
+ goto out;
+
+ ckpt_debug("nfds %d\n", nfds);
+ for (n = 0; n < nfds; n++) {
+ ret = checkpoint_file_desc(ctx, files, fdtable[n]);
+ if (ret < 0)
+ break;
+ }
+ out:
+ kfree(fdtable);
+ return ret;
+}
+
+/* checkpoint callback for file table */
+int checkpoint_file_table(struct ckpt_ctx *ctx, void *ptr)
+{
+ return do_checkpoint_file_table(ctx, (struct files_struct *) ptr);
+}
+
+/* checkpoint wrapper for file table */
+int checkpoint_obj_file_table(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+ struct files_struct *files;
+ int objref;
+
+ files = get_files_struct(t);
+ if (!files)
+ return -EBUSY;
+ objref = checkpoint_obj(ctx, files, CKPT_OBJ_FILE_TABLE);
+ put_files_struct(files);
+
+ return objref;
+}
diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
index 82b4618..ea15958 100644
--- a/checkpoint/objhash.c
+++ b/checkpoint/objhash.c
@@ -13,6 +13,8 @@

#include <linux/kernel.h>
#include <linux/hash.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
#include <linux/checkpoint.h>
#include <linux/checkpoint_hdr.h>

@@ -53,6 +55,28 @@ static int obj_no_grab(void *ptr)
return 0;
}

+static int obj_file_table_grab(void *ptr)
+{
+ atomic_inc(&((struct files_struct *) ptr)->count);
+ return 0;
+}
+
+static void obj_file_table_drop(void *ptr)
+{
+ put_files_struct((struct files_struct *) ptr);
+}
+
+static int obj_file_grab(void *ptr)
+{
+ get_file((struct file *) ptr);
+ return 0;
+}
+
+static void obj_file_drop(void *ptr)
+{
+ fput((struct file *) ptr);
+}
+
static struct ckpt_obj_ops ckpt_obj_ops[] = {
/* ignored object */
{
@@ -61,6 +85,22 @@ static struct ckpt_obj_ops ckpt_obj_ops[] = {
.ref_drop = obj_no_drop,
.ref_grab = obj_no_grab,
},
+ /* files_struct object */
+ {
+ .obj_name = "FILE_TABLE",
+ .obj_type = CKPT_OBJ_FILE_TABLE,
+ .ref_drop = obj_file_table_drop,
+ .ref_grab = obj_file_table_grab,
+ .checkpoint = checkpoint_file_table,
+ },
+ /* file object */
+ {
+ .obj_name = "FILE",
+ .obj_type = CKPT_OBJ_FILE,
+ .ref_drop = obj_file_drop,
+ .ref_grab = obj_file_grab,
+ .checkpoint = checkpoint_file,
+ },
};


diff --git a/checkpoint/process.c b/checkpoint/process.c
index 6cab717..4c922b6 100644
--- a/checkpoint/process.c
+++ b/checkpoint/process.c
@@ -46,6 +46,30 @@ static int checkpoint_task_struct(struct ckpt_ctx *ctx, struct task_struct *t)
return ckpt_write_string(ctx, t->comm, TASK_COMM_LEN);
}

+static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+ struct ckpt_hdr_task_objs *h;
+ int files_objref;
+ int ret;
+
+ files_objref = checkpoint_obj_file_table(ctx, t);
+ ckpt_debug("files: objref %d\n", files_objref);
+ if (files_objref < 0) {
+ ckpt_write_err(ctx, "task %d (%s), files_struct: %d",
+ task_pid_vnr(t), t->comm, files_objref);
+ return files_objref;
+ }
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TASK_OBJS);
+ if (!h)
+ return -ENOMEM;
+ h->files_objref = files_objref;
+ ret = ckpt_write_obj(ctx, &h->h);
+ ckpt_hdr_put(ctx, h);
+
+ return ret;
+}
+
/* dump the entire state of a given task */
int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
{
@@ -55,6 +79,10 @@ int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
ckpt_debug("task %d\n", ret);
if (ret < 0)
goto out;
+ ret = checkpoint_task_objs(ctx, t);
+ ckpt_debug("shared %d\n", ret);
+ if (ret < 0)
+ goto out;
ret = checkpoint_thread(ctx, t);
ckpt_debug("thread %d\n", ret);
if (ret < 0)
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index c8a260d..c2d3d90 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -170,6 +170,7 @@ static void ckpt_ctx_free(struct ckpt_ctx *ctx)
fput(ctx->file);

ckpt_obj_hash_free(ctx);
+ path_put(&ctx->fs_mnt);

kfree(ctx);
}
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 9f65a81..d170988 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -67,14 +67,26 @@ extern int restore_read_header_arch(struct ckpt_ctx *ctx);
extern int restore_thread(struct ckpt_ctx *ctx);
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 checkpoint_file_table(struct ckpt_ctx *ctx, void *ptr);
+
+/* files */
+extern int checkpoint_file(struct ckpt_ctx *ctx, void *ptr);
+
+extern int checkpoint_file_common(struct ckpt_ctx *ctx, struct file *file,
+ struct ckpt_hdr_file *h);
+

/* debugging flags */
#define CKPT_DBASE 0x1 /* anything */
#define CKPT_DSYS 0x2 /* generic (system) */
#define CKPT_DRW 0x4 /* image read/write */
#define CKPT_DOBJ 0x8 /* shared objects */
+#define CKPT_DFILE 0x10 /* files and filesystem */

-#define CKPT_DDEFAULT 0x7 /* default debug level */
+#define CKPT_DDEFAULT 0x17 /* default debug level */

#ifndef CKPT_DFLAG
#define CKPT_DFLAG 0x0 /* nothing */
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 195e44b..5b4fc52 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -47,11 +47,17 @@ enum {
CKPT_HDR_OBJREF,

CKPT_HDR_TASK = 101,
+ CKPT_HDR_TASK_OBJS,
CKPT_HDR_THREAD,
CKPT_HDR_CPU,

/* 201-299: reserved for arch-dependent */

+ CKPT_HDR_FILE_TABLE = 301,
+ CKPT_HDR_FILE_DESC,
+ CKPT_HDR_FILE_NAME,
+ CKPT_HDR_FILE,
+
CKPT_HDR_TAIL = 9001,

CKPT_HDR_ERROR = 9999,
@@ -72,6 +78,8 @@ struct ckpt_hdr_objref {
/* shared objects types */
enum obj_type {
CKPT_OBJ_IGNORE = 0,
+ CKPT_OBJ_FILE_TABLE,
+ CKPT_OBJ_FILE,
CKPT_OBJ_MAX
};

@@ -121,4 +129,45 @@ struct ckpt_hdr_task {
__u32 task_comm_len;
} __attribute__((aligned(8)));

+/* task's shared resources */
+struct ckpt_hdr_task_objs {
+ struct ckpt_hdr h;
+ __s32 files_objref;
+} __attribute__((aligned(8)));
+
+/* file system */
+struct ckpt_hdr_file_table {
+ struct ckpt_hdr h;
+ __s32 fdt_nfds;
+} __attribute__((aligned(8)));
+
+/* file descriptors */
+struct ckpt_hdr_file_desc {
+ struct ckpt_hdr h;
+ __s32 fd_objref;
+ __s32 fd_descriptor;
+ __u32 fd_close_on_exec;
+} __attribute__((aligned(8)));
+
+enum file_type {
+ CKPT_FILE_IGNORE = 0,
+ CKPT_FILE_GENERIC,
+ CKPT_FILE_MAX
+};
+
+/* file objects */
+struct ckpt_hdr_file {
+ struct ckpt_hdr h;
+ __u32 f_type;
+ __u32 f_mode;
+ __u32 f_flags;
+ __u32 _padding;
+ __u64 f_pos;
+ __u64 f_version;
+} __attribute__((aligned(8)));
+
+struct ckpt_hdr_file_generic {
+ struct ckpt_hdr_file common;
+} __attribute__((aligned(8)));
+
#endif /* _CHECKPOINT_CKPT_HDR_H_ */
diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
index 9c14034..067d579 100644
--- a/include/linux/checkpoint_types.h
+++ b/include/linux/checkpoint_types.h
@@ -14,6 +14,12 @@


#ifdef __KERNEL__
+struct ckpt_ctx;
+struct ckpt_hdr_file;
+
+#include <linux/list.h>
+#include <linux/path.h>
+#include <linux/fs.h>

#include <linux/sched.h>

@@ -31,6 +37,8 @@ struct ckpt_ctx {

struct ckpt_obj_hash *obj_hash; /* repository for shared objects */

+ struct path fs_mnt; /* container root (FIXME) */
+
char err_string[256]; /* checkpoint: error string */
};

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 60d9229..e64f892 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2310,7 +2310,11 @@ void inode_sub_bytes(struct inode *inode, loff_t bytes);
loff_t inode_get_bytes(struct inode *inode);
void inode_set_bytes(struct inode *inode, loff_t bytes);

+#ifdef CONFIG_CHECKPOINT
+extern int generic_file_checkpoint(struct ckpt_ctx *ctx, struct file *file);
+#else
#define generic_file_checkpoint NULL
+#endif

extern int vfs_readdir(struct file *, filldir_t, void *);

--
1.6.0.4


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