+ kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files.patch added to -mm tree

+ kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files.patch added to -mm tree

[akpm]

The patch titled
     Subject: kcmp: add KCMP_EPOLL_TFD mode to compare epoll target files
has been added to the -mm tree.  Its filename is
     kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files.patch

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------------------------------------------------------
From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: kcmp: add KCMP_EPOLL_TFD mode to compare epoll target files

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 the target file is present to add it into 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.

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

Link: http://lkml.kernel.org/r/20170424154423.511592110@gmail.com
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrey Vagin <avagin@openvz.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/eventpoll.c            |   42 ++++++++++++++++++++++++++
 include/linux/eventpoll.h |    3 +
 include/uapi/linux/kcmp.h |   10 ++++++
 kernel/kcmp.c             |   57 ++++++++++++++++++++++++++++++++++++
 4 files changed, 112 insertions(+)

diff -puN fs/eventpoll.c~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files fs/eventpoll.c
--- a/fs/eventpoll.c~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files
+++ a/fs/eventpoll.c
@@ -1077,6 +1077,48 @@ 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
diff -puN include/linux/eventpoll.h~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files include/linux/eventpoll.h
--- a/include/linux/eventpoll.h~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files
+++ a/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)
 {
diff -puN include/uapi/linux/kcmp.h~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files include/uapi/linux/kcmp.h
--- a/include/uapi/linux/kcmp.h~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files
+++ a/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 */
+	__u32 toff;		/* target offset within same numbered sequence */
+};
+
 #endif /* _UAPI_LINUX_KCMP_H */
diff -puN kernel/kcmp.c~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files kernel/kcmp.c
--- a/kernel/kcmp.c~kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files
+++ a/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>
 
@@ -94,6 +98,56 @@ static int kcmp_lock(struct mutex *m1, s
 	return err;
 }
 
+#ifdef CONFIG_EPOLL
+static int kcmp_epoll_target(struct task_struct *task1,
+			     struct task_struct *task2,
+			     unsigned long idx1,
+			     struct kcmp_epoll_slot __user *uslot)
+{
+	struct file *filp, *filp_epoll, *filp_tgt;
+	struct kcmp_epoll_slot slot;
+	struct files_struct *files;
+
+	if (copy_from_user(&slot, uslot, sizeof(slot)))
+		return -EFAULT;
+
+	filp = get_file_raw_ptr(task1, idx1);
+	if (!filp)
+		return -EBADF;
+
+	files = get_files_struct(task2);
+	if (!files)
+		return -EBADF;
+
+	spin_lock(&files->file_lock);
+	filp_epoll = fcheck_files(files, slot.efd);
+	if (filp_epoll)
+		get_file(filp_epoll);
+	else
+		filp_tgt = ERR_PTR(-EBADF);
+	spin_unlock(&files->file_lock);
+	put_files_struct(files);
+
+	if (filp_epoll) {
+		filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
+		fput(filp_epoll);
+	} else
+
+	if (IS_ERR(filp_tgt))
+		return PTR_ERR(filp_tgt);
+
+	return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
+}
+#else
+static int kcmp_epoll_target(struct task_struct *task1,
+			     struct task_struct *task2,
+			     unsigned long idx1,
+			     struct kcmp_epoll_slot __user *uslot)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
 		unsigned long, idx1, unsigned long, idx2)
 {
@@ -165,6 +219,9 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t
 		ret = -EOPNOTSUPP;
 #endif
 		break;
+	case KCMP_EPOLL_TFD:
+		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
_

Patches currently in -mm which might be from gorcunov@gmail.com are

procfs-fdinfo-extend-information-about-epoll-target-files.patch
kcmp-add-kcmp_epoll_tfd-mode-to-compare-epoll-target-files.patch