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SubjectRe: [RFC][PATCH 8/8] check files for checkpointability
Quoting Dave Hansen (dave@linux.vnet.ibm.com):
>
> Introduce a files_struct counter to indicate whether a particular
> file_struct has ever contained a file which can not be
> checkpointed. This flag is a one-way trip; once it is set, it may
> not be unset.
>
> We assume at allocation that a new files_struct is clean and may
> be checkpointed. However, as soon as it has had its files filled
> from its parent's, we check it for real in __scan_files_for_cr().
> At that point, we mark it if it contained any uncheckpointable
> files.
>
> We also check each 'struct file' when it is installed in a fd
> slot. This way, if anyone open()s or managed to dup() an
> unsuppored file, we can catch it.
>
> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
> ---
>
> linux-2.6.git-dave/fs/file.c | 19 +++++++++++++++++++
> linux-2.6.git-dave/fs/open.c | 5 +++++
> linux-2.6.git-dave/include/linux/checkpoint.h | 14 ++++++++++++++
> linux-2.6.git-dave/include/linux/fdtable.h | 3 +++
> 4 files changed, 41 insertions(+)
>
> diff -puN fs/file.c~track-files_struct-checkpointability fs/file.c
> --- linux-2.6.git/fs/file.c~track-files_struct-checkpointability 2009-02-27 12:07:41.000000000 -0800
> +++ linux-2.6.git-dave/fs/file.c 2009-02-27 12:07:41.000000000 -0800
> @@ -15,6 +15,7 @@
> #include <linux/file.h>
> #include <linux/fdtable.h>
> #include <linux/bitops.h>
> +#include <linux/checkpoint.h>
> #include <linux/interrupt.h>
> #include <linux/spinlock.h>
> #include <linux/rcupdate.h>
> @@ -285,6 +286,20 @@ static int count_open_files(struct fdtab
> return i;
> }
>
> +static void __scan_files_for_cr(struct files_struct *files)
> +{
> + int i;
> +
> + for (i = 0; i < files->fdtab.max_fds; i++) {
> + struct file *f = fcheck_files(files, i);
> + if (!f)
> + continue;
> + if (cr_file_supported(f))
> + continue;
> + files_deny_checkpointing(files);
> + }
> +}
> +
> /*
> * Allocate a new files structure and copy contents from the
> * passed in files structure.
> @@ -303,6 +318,9 @@ struct files_struct *dup_fd(struct files
> goto out;
>
> atomic_set(&newf->count, 1);
> +#ifdef CONFIG_CHECKPOINT_RESTART
> + newf->may_checkpoint = 1;
> +#endif
>
> spin_lock_init(&newf->file_lock);
> newf->next_fd = 0;
> @@ -396,6 +414,7 @@ struct files_struct *dup_fd(struct files
>
> rcu_assign_pointer(newf->fdt, new_fdt);
>
> + __scan_files_for_cr(newf);
> return newf;
>
> out_release:
> diff -puN fs/open.c~track-files_struct-checkpointability fs/open.c
> --- linux-2.6.git/fs/open.c~track-files_struct-checkpointability 2009-02-27 12:07:41.000000000 -0800
> +++ linux-2.6.git-dave/fs/open.c 2009-02-27 12:07:41.000000000 -0800
> @@ -29,6 +29,7 @@
> #include <linux/rcupdate.h>
> #include <linux/audit.h>
> #include <linux/falloc.h>
> +#include <linux/checkpoint.h>
>
> int vfs_statfs(struct dentry *dentry, struct kstatfs *buf)
> {
> @@ -1015,6 +1016,10 @@ void fd_install(unsigned int fd, struct
> {
> struct files_struct *files = current->files;
> struct fdtable *fdt;
> +
> + if (!cr_file_supported(file))
> + files_deny_checkpointing(files);
> +
> spin_lock(&files->file_lock);
> fdt = files_fdtable(files);
> BUG_ON(fdt->fd[fd] != NULL);
> diff -puN include/linux/checkpoint.h~track-files_struct-checkpointability include/linux/checkpoint.h
> --- linux-2.6.git/include/linux/checkpoint.h~track-files_struct-checkpointability 2009-02-27 12:07:41.000000000 -0800
> +++ linux-2.6.git-dave/include/linux/checkpoint.h 2009-02-27 12:07:41.000000000 -0800
> @@ -12,6 +12,7 @@
>
> #include <linux/path.h>
> #include <linux/fs.h>
> +#include <linux/fdtable.h>
>
> #ifdef CONFIG_CHECKPOINT_RESTART
>
> @@ -102,6 +103,18 @@ extern int cr_read_files(struct cr_ctx *
>
> #define pr_fmt(fmt) "[%d:c/r:%s] " fmt, task_pid_vnr(current), __func__
>
> +static inline void __files_deny_checkpointing(struct files_struct *files,
> + char *file, int line)
> +{
> + if (!test_and_clear_bit(0, &files->may_checkpoint))
> + return;
> + printk(KERN_INFO "process performed an action that can not be "
> + "checkpointed at: %s:%d\n", file, line);
> + WARN_ON(1);

This WARN_ON(1) is one step past the line into obnoxiousness on my
console :)

-serge


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