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authorCyrill Gorcunov <gorcunov@gmail.com>2017-07-13 00:34:28 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-13 02:26:01 +0300
commit0791e3644e5ef21646fe565b9061788d05ec71d4 (patch)
treef16169f6551fe0b2fea513080fcecbe0d4a5cccc /fs/eventpoll.c
parent77493f04b74cdff3a61fb3fb14b1f5a71d88fd5f (diff)
downloadlinux-0791e3644e5ef21646fe565b9061788d05ec71d4.tar.xz
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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/eventpoll.c')
-rw-r--r--fs/eventpoll.c42
1 files changed, 42 insertions, 0 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 322904c3ebdf..e7e9901c3790 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1077,6 +1077,48 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
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