[Devel] Re: [PATCH] Restore task fs_root and pwd (v2)

[Oren Laadan]

Oren Laadan wrote:
> Very necessary !
> See comments inline.
> 
> Serge E. Hallyn wrote:
>> Checkpoint and restore task->fs.  Tasks sharing task->fs will
>> share them again after restart.
>>
>> Changelog:
>> 	Dec 28: Addressed comments by Oren (and Dave)
>> 		1. define and use {get,put}_fs_struct helpers
>> 		2. fix locking comment
>> 		3. define ckpt_read_fname() and use in checkpoint/files.c
>>
>> Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
>> ---
>>  checkpoint/files.c             |  197 +++++++++++++++++++++++++++++++++++++++-
>>  checkpoint/objhash.c           |    9 ++
>>  checkpoint/process.c           |   13 +++
>>  fs/fs_struct.c                 |   21 ++++
>>  fs/open.c                      |   53 ++++++-----
>>  include/linux/checkpoint.h     |   10 ++-
>>  include/linux/checkpoint_hdr.h |   10 ++
>>  include/linux/fs.h             |    4 +
>>  include/linux/fs_struct.h      |    2 +
>>  9 files changed, 293 insertions(+), 26 deletions(-)
>>
>> diff --git a/checkpoint/files.c b/checkpoint/files.c
>> index b622588..d6cf945 100644
>> --- a/checkpoint/files.c
>> +++ b/checkpoint/files.c
>> @@ -24,6 +24,9 @@
>>  #include <linux/checkpoint_hdr.h>
>>  #include <linux/eventpoll.h>
>>  #include <linux/eventfd.h>
>> +#include <linux/fs.h>
>> +#include <linux/fs_struct.h>
>> +#include <linux/namei.h>
>>  #include <net/sock.h>
>>  
>>  
>> @@ -449,10 +452,81 @@ int ckpt_collect_file_table(struct ckpt_ctx *ctx, struct task_struct *t)
>>  	return ret;
>>  }
>>  
>> +int checkpoint_get_task_fs(struct ckpt_ctx *ctx, struct task_struct *t)
> 
> Renaming these to {checkpoint/restore}_obj_filesystem() will be
> consistent with existing naming convention there.
> 
>> +{
>> +	struct fs_struct *fs;
>> +	int fs_objref;
>> +
>> +	task_lock(current);
>> +	fs = t->fs;
>> +	get_fs_struct(fs);
>> +	task_unlock(current);
>> +
>> +	fs_objref = checkpoint_obj(ctx, fs, CKPT_OBJ_TASK_FS);
>> +	put_fs_struct(fs);
>> +
>> +	return fs_objref;
>> +}
>> +
>> +/*
>> + * called with fs refcount bumped so it won't disappear
>> + */
>> +int checkpoint_obj_task_fs(struct ckpt_ctx *ctx, struct fs_struct *fs)
>> +{
>> +	struct ckpt_hdr_task_fs *h;
>> +	int ret;
>> +	struct fs_struct *fscopy;
>> +
>> +	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TASK_FS);
>> +	if (!h)
>> +		return -ENOMEM;
>> +	ret = ckpt_write_obj(ctx, &h->h);
>> +	ckpt_hdr_put(ctx, h);
>> +	if (ret)
>> +		return ret;
>> +
>> +	fscopy = copy_fs_struct(fs);
>> +	if (!fs)
>> +		return -ENOMEM;
>> +
> 
> Reverse the order below: cwd first then root - this will allow
> the cwd to be outside of the current chroot, in the case that
> the task escaped the chroot.
> 
>> +	ret = checkpoint_fname(ctx, &fscopy->root, &ctx->fs_mnt);
>> +	if (ret < 0) {
>> +		ckpt_err(ctx, ret, "%(T)writing name of fs root");
>> +		goto out;
>> +	}
>> +	ret = checkpoint_fname(ctx, &fscopy->pwd, &ctx->fs_mnt);
>> +	if (ret < 0) {
>> +		ckpt_err(ctx, ret, "%(T)writing name of pwd");
>> +		goto out;
>> +	}
>> +	ret = 0;
> 
> [...]
> 
>> +/* this is the fn called by objhash when it runs into a
>> + * CKPT_OBJ_TASK_FS entry.  Creates an fs_struct and
>> + * places it in the hash. */
>> +static struct fs_struct *restore_obj_task_fs(struct ckpt_ctx *ctx)
>> +{
>> +	struct ckpt_hdr_task_fs *h;
>> +	struct fs_struct *fs;
>> +	int ret = 0;
>> +	char *root, *cwd;
>> +
>> +	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TASK_FS);
>> +	if (IS_ERR(h))
>> +		return ERR_PTR(PTR_ERR(h));
>> +	ckpt_hdr_put(ctx, h);
>> +
>> +	fs = copy_fs_struct(current->fs);
>> +	if (!fs)
>> +		return ERR_PTR(-ENOMEM);
>> +
> 
> Please reverse the order below: restore cwd before chroot.
> 
>> +	ret = ckpt_read_fname(ctx, &root);
>> +	if (ret < 0)
>> +		goto out;
>> +	ret = restore_chroot(ctx, fs, root);
>> +	kfree(root);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = ckpt_read_fname(ctx, &cwd);
>> +	if (ret < 0)
>> +		goto out;
>> +	ret = restore_cwd(ctx, fs, cwd);
>> +	kfree(cwd);
>> +
>> +out:
>> +	if (ret) {
>> +		free_fs_struct(fs);
>> +		return ERR_PTR(ret);
>> +	}
>> +	return fs;
>> +}
>> +
>> +void *restore_task_fs(struct ckpt_ctx *ctx)
>> +{
>> +	return (void *) restore_obj_task_fs(ctx);
>> +}
>> +
>> +/*
>> + * Called by task restore code to set the restarted task's
>> + * current->fs to an entry on the hash
>> + */
>> +int restore_set_task_fs(struct ckpt_ctx *ctx, int fs_objref)
> 
> (Please rename this one, too)
> 
>> +{
>> +	struct fs_struct *newfs, *oldfs;
>> +
>> +	newfs = ckpt_obj_fetch(ctx, fs_objref, CKPT_OBJ_TASK_FS);
>> +	if (IS_ERR(newfs))
>> +		return PTR_ERR(newfs);
>> +
>> +	task_lock(current);
>> +	get_fs_struct(newfs);
>> +	oldfs = current->fs;
>> +	current->fs = newfs;
>> +	task_unlock(current);
>> +	put_fs_struct(oldfs);
>> +
>> +	return 0;
>> +}
>> diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
>> index 782661d..20fd3e9 100644
>> --- a/checkpoint/objhash.c
>> +++ b/checkpoint/objhash.c
>> @@ -417,6 +417,15 @@ static struct ckpt_obj_ops ckpt_obj_ops[] = {
>>  		.checkpoint = checkpoint_userns,
>>  		.restore = restore_userns,
>>  	},
>> +	/* struct fs_struct */
>> +	{
>> +		.obj_name = "TASK_FS",
>> +		.obj_type = CKPT_OBJ_TASK_FS,
>> +		.ref_drop = obj_task_fs_drop,
>> +		.ref_grab = obj_task_fs_grab,
>> +		.checkpoint = checkpoint_task_fs,
>> +		.restore = restore_task_fs,
> 
> I think we also need a .collect method to prevent leaks ?

Scratch that.

I meant to ask if we needed more work on collect because the fs
itself points to underlying objects (the path).

But no, because we didn't yet "objectize" the path.

Oren.


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