[RFC v2][PATCH 8/9] File descriprtors - dump state

Oren Laadan orenl at cs.columbia.edu
Wed Aug 20 20:07:16 PDT 2008


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 a
tag and registered in the object hash.

For each open FD there is a 'struct cr_hdr_fd_ent' with the FD, its tag
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 at cs.columbia.edu>
---
  checkpoint/Makefile    |    3 +-
  checkpoint/ckpt.h      |    2 +-
  checkpoint/ckpt_file.c |  234 ++++++++++++++++++++++++++++++++++++++++++++++++
  checkpoint/ckpt_file.h |   17 ++++
  checkpoint/ckpt_hdr.h  |   31 +++++++
  5 files changed, 285 insertions(+), 2 deletions(-)
  create mode 100644 checkpoint/ckpt_file.c
  create mode 100644 checkpoint/ckpt_file.h

diff --git a/checkpoint/Makefile b/checkpoint/Makefile
index cd57d9d..179175b 100644
--- a/checkpoint/Makefile
+++ b/checkpoint/Makefile
@@ -1,2 +1,3 @@
-obj-y += sys.o checkpoint.o restart.o objhash.o ckpt_mem.o rstr_mem.o
+obj-y += sys.o checkpoint.o restart.o objhash.o \
+	ckpt_mem.o rstr_mem.o ckpt_file.o
  obj-$(CONFIG_X86) += ckpt_x86.o rstr_x86.o
diff --git a/checkpoint/ckpt.h b/checkpoint/ckpt.h
index 8b02c4c..ef2f74d 100644
--- a/checkpoint/ckpt.h
+++ b/checkpoint/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 */
diff --git a/checkpoint/ckpt_file.c b/checkpoint/ckpt_file.c
new file mode 100644
index 0000000..18faaf1
--- /dev/null
+++ b/checkpoint/ckpt_file.c
@@ -0,0 +1,234 @@
+/*
+ *  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 "ckpt.h"
+#include "ckpt_hdr.h"
+#include "ckpt_file.h"
+
+#define CR_DEFAULT_FDTABLE  128
+
+/**
+ * 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)
+{
+	int i, j, n, max;
+	struct fdtable *fdt;
+	int *fdlist;
+
+	max = CR_DEFAULT_FDTABLE;
+
+ repeat:
+	fdlist = kmalloc(max * sizeof(*fdlist), GFP_KERNEL);
+	if (!fdlist)
+		return -ENOMEM;
+
+	j = 0;
+	n = 0;
+
+	spin_lock(&files->file_lock);
+	fdt = files_fdtable(files);
+	for (;;) {
+		unsigned long set;
+		i = j * __NFDBITS;
+		if (i >= fdt->max_fds)
+			break;
+		set = fdt->open_fds->fds_bits[j++];
+		while (set) {
+			if (set & 1) {
+				if (unlikely(n == max)) {
+					spin_unlock(&files->file_lock);
+					kfree(fdlist);
+					max *= 2;
+					if (max < 0)	/* overflow ? */
+						return -EMFILE;
+					goto repeat;
+				}
+				fdlist[n++] = i;
+			}
+			i++;
+			set >>= 1;
+		}
+	}
+	spin_unlock(&files->file_lock);
+
+	*fdtable = fdlist;
+	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 ptag)
+{
+	struct cr_hdr h;
+	struct cr_hdr_fd_data *hh = ctx->hbuf;
+	struct dentry *dent = file->f_dentry;
+	struct inode *inode = dent->d_inode;
+	char *fname;
+	int flen, how, ret;
+
+	h.type = CR_HDR_FD_DATA;
+	h.len = sizeof(*hh);
+	h.ptag = ptag;
+
+	BUG_ON(!inode);
+
+	flen = PAGE_SIZE;
+	fname = cr_fill_fname(&file->f_path, ctx->vfsroot, ctx->tbuf, &flen);
+	if (IS_ERR(fname))
+		return PTR_ERR(fname);
+
+	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:
+		how = CR_FD_FILE;
+		break;
+	case S_IFDIR:
+		how = CR_FD_DIR;
+		break;
+	case S_IFLNK:
+		how = CR_FD_LINK;
+		break;
+	default:
+		return -EBADF;
+	}
+
+	/* FIX: check if the file/dir/link is unlinked */
+
+	BUG_ON(!flen);
+
+	ret = cr_write_obj(ctx, &h, hh);
+	if (!ret && flen)
+		ret = cr_write_str(ctx, fname, flen);
+
+	return ret;
+}
+
+/**
+ * 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 tag, 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 = ctx->hbuf;
+	struct file *file = NULL;
+	struct fdtable *fdt;
+	int coe, tag, ret;
+
+	/* make sure hh->fd (that is of type __u16) doesn't overflow */
+	if (fd > USHORT_MAX) {
+		pr_warning("CR: open files table too big (%d)\n", USHORT_MAX);
+		return -EMFILE;
+	}
+
+	rcu_read_lock();
+	fdt = files_fdtable(files);
+	if (fd < fdt->max_fds)
+		file = rcu_dereference(fdt->fd[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 (unlikely(!file))
+		return -EBADF;
+
+	ret = cr_obj_add_ptr(ctx, (void *) file, &tag, CR_OBJ_FILE, 0);
+	cr_debug("fd %d tag %d file %p c-o-e %d)\n", fd, tag, file, coe);
+
+	if (ret >= 0) {
+		int new = ret;
+
+		h.type = CR_HDR_FD_ENT;
+		h.len = sizeof(*hh);
+		h.ptag = 0;
+ 
+		hh->tag = tag;
+		hh->fd = fd;
+		hh->close_on_exec = coe;
+
+		ret = cr_write_obj(ctx, &h, hh);
+
+		/* new==1 if-and-only-if file was new and added to hash */
+		if (!ret && new)
+			ret = cr_write_fd_data(ctx, file, tag);
+	}
+
+	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 = ctx->hbuf;
+	struct files_struct *files;
+	int *fdtable;
+	int nfds, n, ret;
+
+	h.type = CR_HDR_FILES;
+	h.len = sizeof(*hh);
+	h.ptag = task_pid_vnr(t);
+
+	files = get_files_struct(t);
+
+	nfds = cr_scan_fds(files, &fdtable);
+	if (nfds < 0) {
+		ret = nfds;
+		goto out;
+	}
+ 
+	hh->tag = 0;
+	hh->nfds = nfds;
+
+	ret = cr_write_obj(ctx, &h, 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);
+		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/checkpoint/ckpt_hdr.h b/checkpoint/ckpt_hdr.h
index a3919cf..a8a37db 100644
--- a/checkpoint/ckpt_hdr.h
+++ b/checkpoint/ckpt_hdr.h
@@ -43,6 +43,10 @@ enum {
  	CR_HDR_VMA,
  	CR_HDR_MM_CONTEXT,

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

@@ -52,6 +56,13 @@ enum {
  	CR_VMA_FILE
  };

+/* fd subtypes */
+enum {
+	CR_FD_FILE = 1,
+	CR_FD_DIR,
+	CR_FD_LINK
+};
+
  struct cr_hdr_head {
  	__u64 magic;

@@ -114,4 +125,24 @@ struct cr_hdr_vma {

  } __attribute__ ((aligned (8)));

+struct cr_hdr_files {
+	__u32 tag;	/* sharing identifier */
+	__u32 nfds;
+} __attribute__ ((aligned (8)));
+
+struct cr_hdr_fd_ent {
+	__u32 tag;
+	__u16 fd;
+	__u16 close_on_exec;
+} __attribute__ ((aligned (8)));
+
+struct cr_hdr_fd_data {
+	__u16 how;
+	__u16 f_mode;
+	__u32 f_flags;
+	__u32 f_uid, f_gid;
+	__u64 f_pos;
+	__u64 f_version;
+} __attribute__ ((aligned (8)));
+
  #endif /* _CHECKPOINT_CKPT_HDR_H_ */
-- 
1.5.4.3



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