[RFC v8][PATCH 09/12] Dump open file descriptors

Oren Laadan
2008-10-30T13:51:12Z

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.

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

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

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
---
checkpoint/Makefile | 2 +-
checkpoint/checkpoint.c | 4 +
checkpoint/checkpoint_file.h | 17 +++
checkpoint/ckpt_file.c | 232 ++++++++++++++++++++++++++++++++++++++++
include/linux/checkpoint.h | 7 +-
include/linux/checkpoint_hdr.h | 32 ++++++-
6 files changed, 289 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 4cbc9c0..ce622e1 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..5aa295f
--- /dev/null
+++ b/checkpoint/ckpt_file.c
@@ -0,0 +1,232 @@
+/*
+ * 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.
+ *
+ * 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.
+ */
+int cr_scan_fds(struct files_struct *files, int **fdtable)
+{
+ struct fdtable *fdt;
+ int *fds;
+ int i, n = 0;
+ int tot = CR_DEFAULT_FDTABLE;
+
+ fds = kmalloc(tot * sizeof(*fds), GFP_KERNEL);
+ if (!fds)
+ return -ENOMEM;
+
+ /*
+ * We assume that the target task is frozen (or that we checkpoint
+ * ourselves), so we can safely proceed after krealloc() from where
+ * we left off; in the worst cases restart will fail.
+ */
+
+ spin_lock(&files->file_lock);
+ rcu_read_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);
+ rcu_read_unlock();
+ tot *= 2; /* won't overflow: kmalloc will fail */
+ fds = krealloc(fds, tot * sizeof(*fds), GFP_KERNEL);
+ if (!fds) {
+ kfree(fds);
+ return -ENOMEM;
+ }
+ rcu_read_lock();
+ spin_lock(&files->file_lock);
+ }
+ fds[n++] = i;
+ }
+ rcu_read_unlock();
+ 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:
+ cr_hbuf_put(ctx, sizeof(*hh));
+ 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 objref, new, ret;
+ int coe = 0; /* avoid gcc warning */
+
+ 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) {
+ ret = -EBADF;
+ goto out;
+ }
+
+ new = cr_obj_add_ptr(ctx, 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);
+ 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:
+ cr_hbuf_put(ctx, sizeof(*hh));
+ 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);
+
+ nfds = cr_scan_fds(files, &fdtable);
+ if (nfds < 0) {
+ put_files_struct(files);
+ return nfds;
+ }
+
+ hh->objref = 0; /* will be meaningful with multiple processes */
+ 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);
+ put_files_struct(files);
+ return ret;
+}
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index e85b95c..0856b3b 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 */
@@ -79,11 +79,12 @@ 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_ */