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    SubjectRe: [RFC v11][PATCH 05/13] Dump memory address space
    Comments below.

    Oren Laadan wrote:
    > For each VMA, there is a 'struct cr_vma'; if the VMA is file-mapped,
    > it will be followed by the file name. Then comes the actual contents,
    > in one or more chunk: each chunk begins with a header that specifies
    > how many pages it holds, then the virtual addresses of all the dumped
    > pages in that chunk, followed by the actual contents of all dumped
    > pages. A header with zero number of pages marks the end of the contents.
    > Then comes the next VMA and so on.
    >
    > Changelog[v11]:
    > - Copy contents of 'init->fs->root' instead of pointing to them.
    > - Add missing test for VM_MAYSHARE when dumping memory
    >
    > Changelog[v10]:
    > - Acquire dcache_lock around call to __d_path() in cr_fill_name()
    >
    > Changelog[v9]:
    > - Introduce cr_ctx_checkpoint() for checkpoint-specific ctx setup
    > - Test if __d_path() changes mnt/dentry (when crossing filesystem
    > namespace boundary). for now cr_fill_fname() fails the checkpoint.
    >
    > Changelog[v7]:
    > - Fix argument given to kunmap_atomic() in memory dump/restore
    >
    > Changelog[v6]:
    > - Balance all calls to cr_hbuf_get() with matching cr_hbuf_put()
    > (even though it's not really needed)
    >
    > Changelog[v5]:
    > - Improve memory dump code (following Dave Hansen's comments)
    > - Change dump format (and code) to allow chunks of <vaddrs, pages>
    > instead of one long list of each
    > - Fix use of follow_page() to avoid faulting in non-present pages
    >
    > Changelog[v4]:
    > - Use standard list_... for cr_pgarr
    >
    > 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>
    > ---
    > arch/x86/include/asm/checkpoint_hdr.h | 5 +
    > arch/x86/mm/checkpoint.c | 31 ++
    > checkpoint/Makefile | 3 +-
    > checkpoint/checkpoint.c | 88 ++++++
    > checkpoint/checkpoint_arch.h | 2 +
    > checkpoint/checkpoint_mem.h | 41 +++
    > checkpoint/ckpt_mem.c | 503 +++++++++++++++++++++++++++++++++
    > checkpoint/sys.c | 10 +
    > include/linux/checkpoint.h | 12 +
    > include/linux/checkpoint_hdr.h | 32 ++
    > 10 files changed, 726 insertions(+), 1 deletions(-)
    > create mode 100644 checkpoint/checkpoint_mem.h
    > create mode 100644 checkpoint/ckpt_mem.c
    >
    > diff --git a/arch/x86/include/asm/checkpoint_hdr.h b/arch/x86/include/asm/checkpoint_hdr.h
    > index 6325062..33f4c70 100644
    > --- a/arch/x86/include/asm/checkpoint_hdr.h
    > +++ b/arch/x86/include/asm/checkpoint_hdr.h
    > @@ -82,4 +82,9 @@ struct cr_hdr_cpu {
    > /* thread_xstate contents follow (if used_math) */
    > } __attribute__((aligned(8)));
    >
    > +struct cr_hdr_mm_context {
    > + __s16 ldt_entry_size;
    > + __s16 nldt;
    > +} __attribute__((aligned(8)));
    > +
    > #endif /* __ASM_X86_CKPT_HDR__H */
    > diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c
    > index 8dd6d2d..757936e 100644
    > --- a/arch/x86/mm/checkpoint.c
    > +++ b/arch/x86/mm/checkpoint.c
    > @@ -221,3 +221,34 @@ int cr_write_head_arch(struct cr_ctx *ctx)
    >
    > return ret;
    > }
    > +
    > +/* dump the mm->context state */
    > +int cr_write_mm_context(struct cr_ctx *ctx, struct mm_struct *mm, int parent)
    > +{
    > + struct cr_hdr h;
    > + struct cr_hdr_mm_context *hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + int ret;
    > +
    > + h.type = CR_HDR_MM_CONTEXT;
    > + h.len = sizeof(*hh);
    > + h.parent = parent;
    > +
    > + mutex_lock(&mm->context.lock);
    > +
    > + hh->ldt_entry_size = LDT_ENTRY_SIZE;
    > + hh->nldt = mm->context.size;
    > +
    > + cr_debug("nldt %d\n", hh->nldt);
    > +
    > + ret = cr_write_obj(ctx, &h, hh);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + if (ret < 0)
    > + goto out;
    > +
    > + ret = cr_kwrite(ctx, mm->context.ldt,
    > + mm->context.size * LDT_ENTRY_SIZE);

    Do we really want to emit anything under lock? I realize that this
    patch goes and does a ton of writes with mmap_sem held for read -- is
    this ok?

    > +
    > + out:
    > + mutex_unlock(&mm->context.lock);
    > + return ret;
    > +}
    > diff --git a/checkpoint/Makefile b/checkpoint/Makefile
    > index d2df68c..3a0df6d 100644
    > --- a/checkpoint/Makefile
    > +++ b/checkpoint/Makefile
    > @@ -2,4 +2,5 @@
    > # Makefile for linux checkpoint/restart.
    > #
    >
    > -obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o
    > +obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o \
    > + ckpt_mem.o
    > diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
    > index 17cc8d2..56d0ec2 100644
    > --- a/checkpoint/checkpoint.c
    > +++ b/checkpoint/checkpoint.c
    > @@ -13,6 +13,7 @@
    > #include <linux/time.h>
    > #include <linux/fs.h>
    > #include <linux/file.h>
    > +#include <linux/fdtable.h>
    > #include <linux/dcache.h>
    > #include <linux/mount.h>
    > #include <linux/utsname.h>
    > @@ -75,6 +76,66 @@ int cr_write_string(struct cr_ctx *ctx, char *str, int len)
    > return cr_write_obj(ctx, &h, str);
    > }
    >
    > +/**
    > + * cr_fill_fname - return pathname of a given file
    > + * @path: path name
    > + * @root: relative root
    > + * @buf: buffer for pathname
    > + * @n: buffer length (in) and pathname length (out)
    > + */
    > +static char *
    > +cr_fill_fname(struct path *path, struct path *root, char *buf, int *n)
    > +{
    > + struct path tmp = *root;
    > + char *fname;
    > +
    > + BUG_ON(!buf);
    > + spin_lock(&dcache_lock);
    > + fname = __d_path(path, &tmp, buf, *n);
    > + spin_unlock(&dcache_lock);
    > + if (!IS_ERR(fname))
    > + *n = (buf + (*n) - fname);
    > + /*
    > + * FIXME: 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;
    > +}
    > +
    > +/**
    > + * cr_write_fname - write a file name
    > + * @ctx: checkpoint context
    > + * @path: path name
    > + * @root: relative root
    > + */
    > +int cr_write_fname(struct cr_ctx *ctx, struct path *path, struct path *root)
    > +{
    > + struct cr_hdr h;
    > + char *buf, *fname;
    > + int ret, flen;
    > +
    > + flen = PATH_MAX;
    > + buf = kmalloc(flen, GFP_KERNEL);
    > + if (!buf)
    > + return -ENOMEM;
    > +
    > + fname = cr_fill_fname(path, root, buf, &flen);
    > + if (!IS_ERR(fname)) {
    > + h.type = CR_HDR_FNAME;
    > + h.len = flen;
    > + h.parent = 0;
    > + ret = cr_write_obj(ctx, &h, fname);
    > + } else
    > + ret = PTR_ERR(fname);
    > +
    > + kfree(buf);
    > + return ret;
    > +}
    > +
    > /* write the checkpoint header */
    > static int cr_write_head(struct cr_ctx *ctx)
    > {
    > @@ -168,6 +229,10 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
    > cr_debug("task_struct: ret %d\n", ret);
    > if (ret < 0)
    > goto out;
    > + ret = cr_write_mm(ctx, t);
    > + cr_debug("memory: 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)
    > @@ -178,10 +243,33 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
    > return ret;
    > }
    >
    > +static int cr_ctx_checkpoint(struct cr_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;

    Spurious return value?

    > +}
    > +
    > int do_checkpoint(struct cr_ctx *ctx, pid_t pid)
    > {
    > int ret;
    >
    > + ret = cr_ctx_checkpoint(ctx, pid);
    > + if (ret < 0)
    > + goto out;
    > ret = cr_write_head(ctx);
    > if (ret < 0)
    > goto out;
    > diff --git a/checkpoint/checkpoint_arch.h b/checkpoint/checkpoint_arch.h
    > index ada1369..f06c7eb 100644
    > --- a/checkpoint/checkpoint_arch.h
    > +++ b/checkpoint/checkpoint_arch.h
    > @@ -3,6 +3,8 @@
    > extern int cr_write_head_arch(struct cr_ctx *ctx);
    > extern int cr_write_thread(struct cr_ctx *ctx, struct task_struct *t);
    > extern int cr_write_cpu(struct cr_ctx *ctx, struct task_struct *t);
    > +extern int cr_write_mm_context(struct cr_ctx *ctx,
    > + struct mm_struct *mm, int parent);
    >
    > extern int cr_read_head_arch(struct cr_ctx *ctx);
    > extern int cr_read_thread(struct cr_ctx *ctx);
    > diff --git a/checkpoint/checkpoint_mem.h b/checkpoint/checkpoint_mem.h
    > new file mode 100644
    > index 0000000..85546f4
    > --- /dev/null
    > +++ b/checkpoint/checkpoint_mem.h
    > @@ -0,0 +1,41 @@
    > +#ifndef _CHECKPOINT_CKPT_MEM_H_
    > +#define _CHECKPOINT_CKPT_MEM_H_
    > +/*
    > + * Generic container checkpoint-restart
    > + *
    > + * 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/mm_types.h>
    > +
    > +/*
    > + * page-array chains: each cr_pgarr describes a set of <strcut page *,vaddr>

    struct

    > + * tuples (where vaddr is the virtual address of a page in a particular mm).
    > + * Specifically, we use separate arrays so that all vaddrs can be written
    > + * and read at once.
    > + */
    > +
    > +struct cr_pgarr {
    > + unsigned long *vaddrs;
    > + struct page **pages;
    > + unsigned int nr_used;
    > + struct list_head list;
    > +};
    > +
    > +#define CR_PGARR_TOTAL (PAGE_SIZE / sizeof(void *))
    > +#define CR_PGARR_CHUNK (4 * CR_PGARR_TOTAL)
    > +
    > +extern void cr_pgarr_free(struct cr_ctx *ctx);
    > +extern struct cr_pgarr *cr_pgarr_current(struct cr_ctx *ctx);
    > +extern void cr_pgarr_reset_all(struct cr_ctx *ctx);
    > +
    > +static inline int cr_pgarr_is_full(struct cr_pgarr *pgarr)
    > +{
    > + return (pgarr->nr_used == CR_PGARR_TOTAL);
    > +}
    > +
    > +#endif /* _CHECKPOINT_CKPT_MEM_H_ */
    > diff --git a/checkpoint/ckpt_mem.c b/checkpoint/ckpt_mem.c
    > new file mode 100644
    > index 0000000..a2fcdbf
    > --- /dev/null
    > +++ b/checkpoint/ckpt_mem.c
    > @@ -0,0 +1,503 @@
    > +/*
    > + * Checkpoint memory contents
    > + *
    > + * 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/slab.h>
    > +#include <linux/file.h>
    > +#include <linux/pagemap.h>
    > +#include <linux/mm_types.h>
    > +#include <linux/checkpoint.h>
    > +#include <linux/checkpoint_hdr.h>
    > +
    > +#include "checkpoint_arch.h"
    > +#include "checkpoint_mem.h"
    > +
    > +/*
    > + * utilities to alloc, free, and handle 'struct cr_pgarr' (page-arrays)
    > + * (common to ckpt_mem.c and rstr_mem.c).
    > + *
    > + * The checkpoint context structure has two members for page-arrays:
    > + * ctx->pgarr_list: list head of the page-array chain

    What's the second member?

    > + *
    > + * During checkpoint (and restart) the chain tracks the dirty pages (page
    > + * pointer and virtual address) of each MM. For a particular MM, these are
    > + * always added to the head of the page-array chain (ctx->pgarr_list).
    > + * This "current" page-array advances as necessary, and new page-array
    > + * descriptors are allocated on-demand. Before the next chunk of pages,
    > + * the chain is reset but not freed (that is, dereference page pointers).
    > + */
    > +
    > +/* return first page-array in the chain */
    > +static inline struct cr_pgarr *cr_pgarr_first(struct cr_ctx *ctx)
    > +{
    > + if (list_empty(&ctx->pgarr_list))
    > + return NULL;
    > + return list_first_entry(&ctx->pgarr_list, struct cr_pgarr, list);
    > +}
    > +
    > +/* release pages referenced by a page-array */
    > +static void cr_pgarr_release_pages(struct cr_pgarr *pgarr)
    > +{
    > + int i;
    > +
    > + cr_debug("nr_used %d\n", pgarr->nr_used);
    > + /*
    > + * although both checkpoint and restart use 'nr_used', we only
    > + * collect pages during checkpoint; in restart we simply return
    > + */
    > + if (!pgarr->pages)
    > + return;
    > + for (i = pgarr->nr_used; i--; /**/)
    > + page_cache_release(pgarr->pages[i]);

    This is sorta hard to read (and non-intuitive). Is it easier to do:



    for (i = 0; i < pgarr->nr_used; i++)

    page_cache_release(pgarr->pages[i]);


    It shouldn't matter what order you release the pages in..

    > +}
    > +
    > +/* free a single page-array object */
    > +static void cr_pgarr_free_one(struct cr_pgarr *pgarr)
    > +{
    > + cr_pgarr_release_pages(pgarr);
    > + kfree(pgarr->pages);
    > + kfree(pgarr->vaddrs);
    > + kfree(pgarr);
    > +}
    > +
    > +/* free a chain of page-arrays */
    > +void cr_pgarr_free(struct cr_ctx *ctx)
    > +{
    > + struct cr_pgarr *pgarr, *tmp;
    > +
    > + list_for_each_entry_safe(pgarr, tmp, &ctx->pgarr_list, list) {
    > + list_del(&pgarr->list);
    > + cr_pgarr_free_one(pgarr);
    > + }
    > +}
    > +
    > +/* allocate a single page-array object */
    > +static struct cr_pgarr *cr_pgarr_alloc_one(unsigned long flags)
    > +{
    > + struct cr_pgarr *pgarr;
    > +
    > + pgarr = kzalloc(sizeof(*pgarr), GFP_KERNEL);
    > + if (!pgarr)
    > + return NULL;
    > +
    > + pgarr->vaddrs = kmalloc(CR_PGARR_TOTAL * sizeof(unsigned long),
    You used PAGE_SIZE / sizeof(void *) above. Why not __get_free_page()?

    > + GFP_KERNEL);
    > + if (!pgarr->vaddrs)
    > + goto nomem;
    > +
    > + /* pgarr->pages is needed only for checkpoint */
    > + if (flags & CR_CTX_CKPT) {
    > + pgarr->pages = kmalloc(CR_PGARR_TOTAL * sizeof(struct page *),
    > + GFP_KERNEL);
    > + if (!pgarr->pages)
    > + goto nomem;
    > + }
    > +
    > + return pgarr;
    > +
    > + nomem:
    > + cr_pgarr_free_one(pgarr);
    > + return NULL;
    > +}
    > +
    > +/* cr_pgarr_current - return the next available page-array in the chain
    > + * @ctx: checkpoint context
    > + *
    > + * Returns the first page-array in the list that has space. Extends the
    > + * list if none has space.
    > + */
    > +struct cr_pgarr *cr_pgarr_current(struct cr_ctx *ctx)
    > +{
    > + struct cr_pgarr *pgarr;
    > +
    > + pgarr = cr_pgarr_first(ctx);
    > + if (pgarr && !cr_pgarr_is_full(pgarr))
    > + goto out;
    > + pgarr = cr_pgarr_alloc_one(ctx->flags);
    > + if (!pgarr)
    > + goto out;
    > + list_add(&pgarr->list, &ctx->pgarr_list);
    > + out:
    > + return pgarr;
    > +}
    > +
    > +/* reset the page-array chain (dropping page references if necessary) */
    > +void cr_pgarr_reset_all(struct cr_ctx *ctx)
    > +{
    > + struct cr_pgarr *pgarr;
    > +
    > + list_for_each_entry(pgarr, &ctx->pgarr_list, list) {
    > + cr_pgarr_release_pages(pgarr);
    > + pgarr->nr_used = 0;
    > + }

    This doesn't look right. cr_pgarr_current only ever looks at the head
    of the list, so resetting a list with > 1 pgarr on it will mean the
    non-head elements in the list will go to waste.

    > +}
    > +
    > +/*
    > + * Checkpoint is outside the context of the checkpointee, so one cannot
    > + * simply read pages from user-space. Instead, we scan the address space
    > + * of the target to cherry-pick pages of interest. Selected pages are
    > + * enlisted in a page-array chain (attached to the checkpoint context).
    > + * To save their contents, each page is mapped to kernel memory and then
    > + * dumped to the file descriptor.
    > + */
    > +
    > +
    > +/**
    > + * cr_private_follow_page - return page pointer for dirty pages
    > + * @vma - target vma
    > + * @addr - page address
    > + *
    > + * Looks up the page that correspond to the address in the vma, and
    > + * returns the page if it was modified (and grabs a reference to it),
    > + * or otherwise returns NULL (or error).
    > + *
    > + * This function should _only_ called for private vma's.
    > + */
    > +static struct page *
    > +cr_private_follow_page(struct vm_area_struct *vma, unsigned long addr)

    s/cr_private_follow_page/cr_follow_page_private/ ?

    Maybe even cr_dump_private_page? The fact that it's following the page
    tables down to the page is an implementation artifact and isn't really
    relevant to the semantics you want to express.

    > +{
    > + struct page *page;
    > +
    > + BUG_ON(vma->vm_flags & (VM_SHARED | VM_MAYSHARE));
    > +

    This BUG_ON shouldn't be needed if it's already done in
    cr_private_vma_fill_pgarr.

    > + /*
    > + * simplified version of get_user_pages(): already have vma,
    > + * only need FOLL_ANON, and (for now) ignore fault stats.
    > + *
    > + * follow_page() will return NULL if the page is not present
    > + * (swapped), ZERO_PAGE(0) if the pte wasn't allocated, and
    > + * the actual page pointer otherwise.
    > + *
    > + * FIXME: consolidate with get_user_pages()
    > + */
    > +
    > + cond_resched();
    > + while (!(page = follow_page(vma, addr, FOLL_ANON | FOLL_GET))) {
    > + int ret;
    > +
    > + /* the page is swapped out - bring it in (optimize ?) */
    > + ret = handle_mm_fault(vma->vm_mm, vma, addr, 0);
    > + if (ret & VM_FAULT_ERROR) {
    > + if (ret & VM_FAULT_OOM)
    > + return ERR_PTR(-ENOMEM);
    > + else if (ret & VM_FAULT_SIGBUS)
    > + return ERR_PTR(-EFAULT);
    > + else
    > + BUG();
    > + break;
    > + }
    > + cond_resched();
    > + }
    > +
    > + if (IS_ERR(page))
    > + return page;
    > +
    > + /*
    > + * We only care about dirty pages: either non-zero page, or
    > + * file-backed (copy-on-write) that were touched. For the latter,
    > + * the page_mapping() will be unset because it will no longer be
    > + * mapped to the original file after having been modified.
    > + */
    > + if (page == ZERO_PAGE(0)) {
    > + /* this is the zero page: ignore */
    > + page_cache_release(page);
    > + page = NULL;
    > + } else if (vma->vm_file && (page_mapping(page) != NULL)) {
    > + /* file backed clean cow: ignore */

    Probably better to describe 'why' it can be ignored here.


    > + page_cache_release(page);
    > + page = NULL;
    > + }
    > +
    > + return page;
    > +}
    > +
    > +/**
    > + * cr_private_vma_fill_pgarr - fill a page-array with addr/page tuples
    > + * @ctx - checkpoint context
    > + * @pgarr - page-array to fill
    > + * @vma - vma to scan
    > + * @start - start address (updated)
    > + *
    > + * Returns the number of pages collected
    > + */
    > +static int
    > +cr_private_vma_fill_pgarr(struct cr_ctx *ctx, struct cr_pgarr *pgarr,
    > + struct vm_area_struct *vma, unsigned long *start)

    This is sorta nasty because you shouldn't need to call into this routine
    with a container. It should be able to enqueue the (vaddr, page) tuple
    directly on the ctx. Doing so would also abstract out the pgarr
    management at this level and make the code a lot simpler.

    > +{
    > + unsigned long end = vma->vm_end;
    > + unsigned long addr = *start;
    > + int orig_used = pgarr->nr_used;
    > +
    > + /* this function is only for private memory (anon or file-mapped) */
    > + BUG_ON(vma->vm_flags & (VM_SHARED | VM_MAYSHARE));
    > +
    > + while (addr < end) {
    > + struct page *page;
    > +
    > + page = cr_private_follow_page(vma, addr);
    > + if (IS_ERR(page))
    > + return PTR_ERR(page);
    > +
    > + if (page) {
    > + pgarr->pages[pgarr->nr_used] = page;
    > + pgarr->vaddrs[pgarr->nr_used] = addr;
    > + pgarr->nr_used++;

    Should be something like:

    ret = cr_ctx_append_page(ctx, addr, page);
    if (ret < 0)
    goto out;

    > + }
    > +
    > + addr += PAGE_SIZE;
    > +
    > + if (cr_pgarr_is_full(pgarr))
    > + break;
    > + }
    > +
    > + *start = addr;
    > + return pgarr->nr_used - orig_used;
    > +}
    > +
    > +/* dump contents of a pages: use kmap_atomic() to avoid TLB flush */
    > +static int cr_page_write(struct cr_ctx *ctx, struct page *page, char *buf)
    > +{
    > + void *ptr;
    > +
    > + ptr = kmap_atomic(page, KM_USER1);
    > + memcpy(buf, ptr, PAGE_SIZE);
    > + kunmap_atomic(ptr, KM_USER1);
    > +
    > + return cr_kwrite(ctx, buf, PAGE_SIZE);
    > +}
    > +
    > +/**
    > + * cr_vma_dump_pages - dump pages listed in the ctx page-array chain
    > + * @ctx - checkpoint context
    > + * @total - total number of pages
    > + *
    > + * First dump all virtual addresses, followed by the contents of all pages
    > + */
    > +static int cr_vma_dump_pages(struct cr_ctx *ctx, int total)
    > +{
    > + struct cr_pgarr *pgarr;
    > + char *buf;
    > + int i, ret = 0;
    > +
    > + if (!total)
    > + return 0;
    > +
    > + list_for_each_entry_reverse(pgarr, &ctx->pgarr_list, list) {
    > + ret = cr_kwrite(ctx, pgarr->vaddrs,
    > + pgarr->nr_used * sizeof(*pgarr->vaddrs));
    > + if (ret < 0)
    > + return ret;
    > + }
    > +
    > + buf = kmalloc(PAGE_SIZE, GFP_KERNEL);

    __get_free_page()

    > + if (!buf)
    > + return -ENOMEM;
    > +
    > + list_for_each_entry_reverse(pgarr, &ctx->pgarr_list, list) {
    > + for (i = 0; i < pgarr->nr_used; i++) {
    > + ret = cr_page_write(ctx, pgarr->pages[i], buf);
    > + if (ret < 0)
    > + goto out;
    > + }
    > + }
    > +
    > + out:
    > + kfree(buf);
    > + return ret;
    > +}
    > +
    > +/**
    > + * cr_write_private_vma_contents - dump contents of a VMA with private memory
    > + * @ctx - checkpoint context
    > + * @vma - vma to scan
    > + *
    > + * Collect lists of pages that needs to be dumped, and corresponding
    > + * virtual addresses into ctx->pgarr_list page-array chain. Then dump
    > + * the addresses, followed by the page contents.
    > + */
    > +static int
    > +cr_write_private_vma_contents(struct cr_ctx *ctx, struct vm_area_struct *vma)
    > +{
    > + struct cr_hdr h;
    > + struct cr_hdr_pgarr *hh;
    > + unsigned long addr = vma->vm_start;
    > + struct cr_pgarr *pgarr;
    > + unsigned long cnt = 0;
    > + int ret;
    > +
    > + /*
    > + * Work iteratively, collecting and dumping at most CR_PGARR_CHUNK
    > + * in each round. Each iterations is divided into two steps:
    > + *
    > + * (1) scan: scan through the PTEs of the vma to collect the pages
    > + * to dump (later we'll also make them COW), while keeping a list
    > + * of pages and their corresponding addresses on ctx->pgarr_list.
    > + *
    > + * (2) dump: write out a header specifying how many pages, followed
    > + * by the addresses of all pages in ctx->pgarr_list, followed by
    > + * the actual contents of all pages. (Then, release the references
    > + * to the pages and reset the page-array chain).
    > + *
    > + * (This split makes the logic simpler by first counting the pages
    > + * that need saving. More importantly, it allows for a future
    > + * optimization that will reduce application downtime by deferring
    > + * the actual write-out of the data to after the application is
    > + * allowed to resume execution).
    > + *
    > + * After dumpting the entire contents, conclude with a header that
    > + * specifies 0 pages to mark the end of the contents.
    > + */
    > +
    > + h.type = CR_HDR_PGARR;
    > + h.len = sizeof(*hh);
    > + h.parent = 0;
    > +
    > + while (addr < vma->vm_end) {
    > + pgarr = cr_pgarr_current(ctx);
    > + if (!pgarr)
    > + return -ENOMEM;
    > + ret = cr_private_vma_fill_pgarr(ctx, pgarr, vma, &addr);
    > + if (ret < 0)
    > + return ret;
    > + cnt += ret;
    > +
    > + /* did we complete a chunk, or is this the last chunk ? */
    > + if (cnt >= CR_PGARR_CHUNK || (cnt && addr == vma->vm_end)) {
    > + hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + hh->nr_pages = cnt;
    > + ret = cr_write_obj(ctx, &h, hh);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + if (ret < 0)
    > + return ret;
    > +
    > + ret = cr_vma_dump_pages(ctx, cnt);
    > + if (ret < 0)
    > + return ret;
    > +
    > + cr_pgarr_reset_all(ctx);
    > + }
    > + }
    > +
    > + /* mark end of contents with header saying "0" pages */
    > + hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + hh->nr_pages = 0;
    > + ret = cr_write_obj(ctx, &h, hh);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > +
    > + return ret;
    > +}
    > +
    > +static int cr_write_vma(struct cr_ctx *ctx, struct vm_area_struct *vma)
    > +{
    > + struct cr_hdr h;
    > + struct cr_hdr_vma *hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + int vma_type, ret;
    > +
    > + h.type = CR_HDR_VMA;
    > + h.len = sizeof(*hh);
    > + h.parent = 0;
    > +
    > + hh->vm_start = vma->vm_start;
    > + hh->vm_end = vma->vm_end;
    > + hh->vm_page_prot = vma->vm_page_prot.pgprot;
    > + hh->vm_flags = vma->vm_flags;
    > + hh->vm_pgoff = vma->vm_pgoff;
    > +
    > +#define CR_BAD_VM_FLAGS \
    > + (VM_SHARED | VM_MAYSHARE | VM_IO | VM_HUGETLB | VM_NONLINEAR)
    > +
    > + if (vma->vm_flags & CR_BAD_VM_FLAGS) {
    > + pr_warning("c/r: unsupported VMA %#lx\n", vma->vm_flags);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + return -ENOSYS;
    > + }
    > +

    The following code should be broken into it's own function? Handling of
    other types of memory will follow and will clutter this guy up.

    > + /* by default assume anon memory */
    > + vma_type = CR_VMA_ANON;
    > +
    > + /*
    > + * if there is a backing file, assume private-mapped

    Shouldn't need to assume anything as you checked for VM_MAYSHARE and
    VM_SHARED above.

    > + * (FIXME: check if the file is unlinked)
    > + */
    > + if (vma->vm_file)
    > + vma_type = CR_VMA_FILE;
    > +
    > + hh->vma_type = vma_type;
    > +
    > + ret = cr_write_obj(ctx, &h, hh);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + if (ret < 0)
    > + return ret;
    > +
    > + /* save the file name, if relevant */

    s/, if relevant//

    > + if (vma->vm_file) {
    > + ret = cr_write_fname(ctx, &vma->vm_file->f_path, &ctx->fs_mnt);

    Why is this using a filename, rather than a reference to a file?
    Shouldn't this use the logic in patch 8/13?

    > + if (ret < 0)
    > + return ret;
    > + }
    > +
    > + return cr_write_private_vma_contents(ctx, vma);
    > +}
    > +
    > +int cr_write_mm(struct cr_ctx *ctx, struct task_struct *t)
    > +{
    > + struct cr_hdr h;
    > + struct cr_hdr_mm *hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + struct mm_struct *mm;
    > + struct vm_area_struct *vma;
    > + int objref, ret;
    > +
    > + h.type = CR_HDR_MM;
    > + h.len = sizeof(*hh);
    > + h.parent = task_pid_vnr(t);
    > +
    > + mm = get_task_mm(t);
    > +
    > + objref = 0; /* will be meaningful with multiple processes */
    > + hh->objref = objref;
    > +
    > + down_read(&mm->mmap_sem);
    > +
    > + hh->start_code = mm->start_code;
    > + hh->end_code = mm->end_code;
    > + hh->start_data = mm->start_data;
    > + hh->end_data = mm->end_data;
    > + hh->start_brk = mm->start_brk;
    > + hh->brk = mm->brk;
    > + hh->start_stack = mm->start_stack;
    > + hh->arg_start = mm->arg_start;
    > + hh->arg_end = mm->arg_end;
    > + hh->env_start = mm->env_start;
    > + hh->env_end = mm->env_end;
    > +
    > + hh->map_count = mm->map_count;
    > +
    > + /* FIX: need also mm->flags */
    > +
    > + ret = cr_write_obj(ctx, &h, hh);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + if (ret < 0)
    > + goto out;
    > +
    > + /* write the vma's */
    > + for (vma = mm->mmap; vma; vma = vma->vm_next) {
    > + ret = cr_write_vma(ctx, vma);
    > + if (ret < 0)
    > + goto out;
    > + }
    > +
    > + ret = cr_write_mm_context(ctx, mm, objref);
    > +
    > + out:
    > + up_read(&mm->mmap_sem);
    > + mmput(mm);
    > + return ret;
    > +}
    > diff --git a/checkpoint/sys.c b/checkpoint/sys.c
    > index bd14ef9..c547a1c 100644
    > --- a/checkpoint/sys.c
    > +++ b/checkpoint/sys.c
    > @@ -16,6 +16,8 @@
    > #include <linux/capability.h>
    > #include <linux/checkpoint.h>
    >
    > +#include "checkpoint_mem.h"
    > +
    > /*
    > * Helpers to write(read) from(to) kernel space to(from) the checkpoint
    > * image file descriptor (similar to how a core-dump is performed).
    > @@ -131,7 +133,13 @@ static void cr_ctx_free(struct cr_ctx *ctx)
    > {
    > if (ctx->file)
    > fput(ctx->file);
    > +
    > kfree(ctx->hbuf);
    > +
    > + path_put(&ctx->fs_mnt); /* safe with NULL pointers */
    > +
    > + cr_pgarr_free(ctx);
    > +
    > kfree(ctx);
    > }
    >
    > @@ -146,6 +154,8 @@ static struct cr_ctx *cr_ctx_alloc(int fd, unsigned long flags)
    >
    > ctx->flags = flags;
    >
    > + INIT_LIST_HEAD(&ctx->pgarr_list);
    > +
    > err = -EBADF;
    > ctx->file = fget(fd);
    > if (!ctx->file)
    > diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
    > index 63f298f..4e97f9f 100644
    > --- a/include/linux/checkpoint.h
    > +++ b/include/linux/checkpoint.h
    > @@ -10,6 +10,9 @@
    > * distribution for more details.
    > */
    >
    > +#include <linux/path.h>
    > +#include <linux/fs.h>
    > +
    > #define CR_VERSION 1
    >
    > struct cr_ctx {
    > @@ -25,6 +28,10 @@ struct cr_ctx {
    >
    > void *hbuf; /* temporary buffer for headers */
    > int hpos; /* position in headers buffer */
    > +
    > + struct list_head pgarr_list; /* page array to dump VMA contents */
    > +
    > + struct path fs_mnt; /* container root (FIXME) */
    > };
    >
    > /* cr_ctx: flags */
    > @@ -42,6 +49,8 @@ struct cr_hdr;
    > extern int cr_write_obj(struct cr_ctx *ctx, struct cr_hdr *h, void *buf);
    > extern int cr_write_buffer(struct cr_ctx *ctx, void *buf, int len);
    > extern int cr_write_string(struct cr_ctx *ctx, char *str, int len);
    > +extern int cr_write_fname(struct cr_ctx *ctx,
    > + struct path *path, struct path *root);
    >
    > extern int cr_read_obj(struct cr_ctx *ctx, struct cr_hdr *h, void *buf, int n);
    > extern int cr_read_obj_type(struct cr_ctx *ctx, void *buf, int len, int type);
    > @@ -50,7 +59,10 @@ extern int cr_read_buffer(struct cr_ctx *ctx, void *buf, int *len);
    > extern int cr_read_string(struct cr_ctx *ctx, char *str, int len);
    >
    > extern int do_checkpoint(struct cr_ctx *ctx, pid_t pid);
    > +extern int cr_write_mm(struct cr_ctx *ctx, struct task_struct *t);
    > +
    > extern int do_restart(struct cr_ctx *ctx, pid_t pid);
    > +extern int cr_read_mm(struct cr_ctx *ctx);
    >
    > #define cr_debug(fmt, args...) \
    > pr_debug("[%d:c/r:%s] " fmt, task_pid_vnr(current), __func__, ## args)
    > diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
    > index b74b5f9..d78f0f1 100644
    > --- a/include/linux/checkpoint_hdr.h
    > +++ b/include/linux/checkpoint_hdr.h
    > @@ -34,6 +34,7 @@ enum {
    > CR_HDR_HEAD_ARCH,
    > CR_HDR_BUFFER,
    > CR_HDR_STRING,
    > + CR_HDR_FNAME,
    >
    > CR_HDR_TASK = 101,
    > CR_HDR_THREAD,
    > @@ -41,6 +42,7 @@ enum {
    >
    > CR_HDR_MM = 201,
    > CR_HDR_VMA,
    > + CR_HDR_PGARR,
    > CR_HDR_MM_CONTEXT,
    >
    > CR_HDR_TAIL = 5001
    > @@ -75,4 +77,34 @@ struct cr_hdr_task {
    > __s32 task_comm_len;
    > } __attribute__((aligned(8)));
    >
    > +struct cr_hdr_mm {
    > + __u32 objref; /* identifier for shared objects */
    > + __u32 map_count;
    > +
    > + __u64 start_code, end_code, start_data, end_data;
    > + __u64 start_brk, brk, start_stack;
    > + __u64 arg_start, arg_end, env_start, env_end;
    > +} __attribute__((aligned(8)));
    > +
    > +/* vma subtypes */
    > +enum vm_type {
    > + CR_VMA_ANON = 1,
    > + CR_VMA_FILE

    We need to figure out what MAP_SHARED | MAP_ANONYMOUS should be exposed
    as in this setup (much in the same way we need to start defining what
    shm mappings look like). Internally, they are 'file-backed', but to
    userland, they aren't.


    Thoughts?

    > +};
    > +
    > +struct cr_hdr_vma {
    > + __u32 vma_type;
    > + __u32 _padding;
    Why padding?

    > +
    > + __u64 vm_start;
    > + __u64 vm_end;
    > + __u64 vm_page_prot;
    > + __u64 vm_flags;
    > + __u64 vm_pgoff;
    > +} __attribute__((aligned(8)));
    > +
    > +struct cr_hdr_pgarr {
    > + __u64 nr_pages; /* number of pages to saved */
    > +} __attribute__((aligned(8)));
    > +
    > #endif /* _CHECKPOINT_CKPT_HDR_H_ */



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