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Date: Mon, 27 Feb 2017 14:43:47 -0800
From: Andrei Vagin <avagin@...tuozzo.com>
To: Cyrill Gorcunov <gorcunov@...nvz.org>
CC: <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-api@...r.kernel.org>, <viro@...iv.linux.org.uk>,
<akpm@...uxfoundation.org>, <xemul@...tuozzo.com>,
<mtk.manpages@...il.com>, <kir@...nvz.org>, <luto@...capital.net>,
<jbaron@...mai.com>, Andrey Vagin <avagin@...nvz.org>
Subject: Re: [RFC 2/3] kcmp: Add KCMP_EPOLL_TFD mode to compare epoll target
files
On Tue, Feb 21, 2017 at 07:59:46PM +0300, Cyrill Gorcunov wrote:
> With current epoll architecture target files are addressed
> with file_struct and file descriptor number, where the last
> is not unique. Moreover files can be transferred from another
> process via unix socket, added into queue and closed then
> so we won't find this descriptor in the task fdinfo list.
>
> Thus to checkpoint and restore such processes CRIU needs to
> find out where exactly target file is present to add it into
> the epoll queue. For this sake one can use kcmp call where
> some particular target file from the queue is compared with
> arbitrary file passed as an argument.
>
> Because epoll target files can have same file descriptor
> number but different file_struct a caller should explicitly
> specify the offset within such entries.
>
> To test if some particular file is matching entry inside
> epoll one have to
>
> - fill kcmp_epoll_slot structure with epoll file descriptor,
> target file number and target file offset (in case if only
> one target is present then it should be 0)
>
> - call kcmp as kcmp(pid1, pid2, KCMP_EPOLL_TFD, fd, &kcmp_epoll_slot)
> - the kernel fetch file pointer matching file descriptor @fd of pid1
> - lookups for file struct in epoll queue of pid2 and returns traditional
> 0,1,2 result for sorting purpose
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> CC: Al Viro <viro@...iv.linux.org.uk>
> CC: Andrew Morton <akpm@...uxfoundation.org>
> CC: Andrey Vagin <avagin@...nvz.org>
> CC: Pavel Emelyanov <xemul@...tuozzo.com>
> CC: Michael Kerrisk <mtk.manpages@...il.com>
> CC: Kir Kolyshkin <kir@...nvz.org>
> CC: Jason Baron <jbaron@...mai.com>
> CC: Andy Lutomirski <luto@...capital.net>
> ---
> fs/eventpoll.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/eventpoll.h | 3 +++
> include/uapi/linux/kcmp.h | 10 ++++++++++
> kernel/kcmp.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 99 insertions(+)
>
> Index: linux-ml.git/fs/eventpoll.c
> ===================================================================
> --- linux-ml.git.orig/fs/eventpoll.c
> +++ linux-ml.git/fs/eventpoll.c
> @@ -1000,6 +1000,48 @@ static struct epitem *ep_find(struct eve
> return epir;
> }
>
> +static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
> +{
> + struct rb_node *rbp;
> + struct epitem *epi;
> +
> + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
> + epi = rb_entry(rbp, struct epitem, rbn);
> + if (epi->ffd.fd == tfd) {
> + if (toff == 0)
> + return epi;
> + else
> + toff--;
> + }
> + cond_resched();
> + }
> +
> + return NULL;
> +}
> +
> +struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
> + unsigned long toff)
> +{
> + struct file *file_raw;
> + struct eventpoll *ep;
> + struct epitem *epi;
> +
> + if (!is_file_epoll(file))
> + return ERR_PTR(-EINVAL);
> +
> + ep = file->private_data;
> +
> + mutex_lock(&ep->mtx);
> + epi = ep_find_tfd(ep, tfd, toff);
> + if (epi)
> + file_raw = epi->ffd.file;
> + else
> + file_raw = ERR_PTR(-ENOENT);
> + mutex_unlock(&ep->mtx);
> +
> + return file_raw;
> +}
> +
> /*
> * This is the callback that is passed to the wait queue wakeup
> * mechanism. It is called by the stored file descriptors when they
> Index: linux-ml.git/include/linux/eventpoll.h
> ===================================================================
> --- linux-ml.git.orig/include/linux/eventpoll.h
> +++ linux-ml.git/include/linux/eventpoll.h
> @@ -14,6 +14,7 @@
> #define _LINUX_EVENTPOLL_H
>
> #include <uapi/linux/eventpoll.h>
> +#include <uapi/linux/kcmp.h>
>
>
> /* Forward declarations to avoid compiler errors */
> @@ -22,6 +23,8 @@ struct file;
>
> #ifdef CONFIG_EPOLL
>
> +struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long toff);
> +
> /* Used to initialize the epoll bits inside the "struct file" */
> static inline void eventpoll_init_file(struct file *file)
> {
> Index: linux-ml.git/include/uapi/linux/kcmp.h
> ===================================================================
> --- linux-ml.git.orig/include/uapi/linux/kcmp.h
> +++ linux-ml.git/include/uapi/linux/kcmp.h
> @@ -1,6 +1,8 @@
> #ifndef _UAPI_LINUX_KCMP_H
> #define _UAPI_LINUX_KCMP_H
>
> +#include <linux/types.h>
> +
> /* Comparison type */
> enum kcmp_type {
> KCMP_FILE,
> @@ -10,8 +12,16 @@ enum kcmp_type {
> KCMP_SIGHAND,
> KCMP_IO,
> KCMP_SYSVSEM,
> + KCMP_EPOLL_TFD,
>
> KCMP_TYPES,
> };
>
> +/* Slot for KCMP_EPOLL_TFD */
> +struct kcmp_epoll_slot {
> + __u32 efd; /* epoll file descriptor */
> + __u32 tfd; /* target file number */
> + __u64 toff; /* target offset within same numbered sequence */
> +};
> +
> #endif /* _UAPI_LINUX_KCMP_H */
> Index: linux-ml.git/kernel/kcmp.c
> ===================================================================
> --- linux-ml.git.orig/kernel/kcmp.c
> +++ linux-ml.git/kernel/kcmp.c
> @@ -11,6 +11,10 @@
> #include <linux/bug.h>
> #include <linux/err.h>
> #include <linux/kcmp.h>
> +#include <linux/capability.h>
> +#include <linux/list.h>
> +#include <linux/eventpoll.h>
> +#include <linux/file.h>
>
> #include <asm/unistd.h>
>
> @@ -165,6 +169,46 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t
> ret = -EOPNOTSUPP;
> #endif
> break;
> + case KCMP_EPOLL_TFD: {
> +#ifdef CONFIG_EPOLL
> + struct file *filp1, *filp_epoll, *filp_tgt;
> + struct kcmp_epoll_slot slot;
> + struct files_struct *files;
> +
> + if (copy_from_user(&slot, (void *)idx2, sizeof(slot))) {
> + ret = -EFAULT;
> + goto err_unlock;
> + }
> +
> + filp1 = get_file_raw_ptr(task1, idx1);
> +
> + files = get_files_struct(task2);
> + if (files) {
> + spin_lock(&files->file_lock);
> + filp_epoll = fcheck_files(files, slot.efd);
> + if (filp_epoll)
> + get_file(filp_epoll);
> + spin_unlock(&files->file_lock);
> + put_files_struct(files);
> + } else
> + filp_epoll = NULL;
> +
> + if (filp1 && filp_epoll) {
> + filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
> + if (IS_ERR(filp_tgt))
> + ret = PTR_ERR(filp_tgt);
> + else
> + ret = kcmp_ptr(filp1, filp_tgt, KCMP_EPOLL_TFD);
I think KCMP_FILE has to be used here ^^^^, because we compare files. We
have to use the same function for all files to be able to sort them, don't we?
> + } else
> + ret = -EBADF;
> +
> + if (filp_epoll)
> + fput(filp_epoll);
> +#else
> + ret = -EOPNOTSUPP;
> +#endif
> + break;
> + }
> default:
> ret = -EINVAL;
> break;
>
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