The ability to check open file descriptions for equality (without
resorting to unreliable fstat() and fcntl(F_GETFL) comparisons) can be
useful outside of the checkpoint/restore use case - for example,
systemd uses kcmp() to deduplicate the per-service file descriptor
store.
Make it possible to have the kcmp() syscall without the full
CONFIG_CHECKPOINT_RESTORE.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
I deliberately drop the ifdef in the eventpoll.h header rather than
replace with KCMP_SYSCALL; it's harmless to declare a function that
isn't defined anywhere.
fs/eventpoll.c | 4 ++--
include/linux/eventpoll.h | 2 --
init/Kconfig | 11 +++++++++++
kernel/Makefile | 2 +-
4 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 12eebcdea9c8..b0313ce2df73 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1064,7 +1064,7 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
return epir;
}
-#ifdef CONFIG_CHECKPOINT_RESTORE
+#ifdef CONFIG_KCMP_SYSCALL
static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
{
struct rb_node *rbp;
@@ -1106,7 +1106,7 @@ struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
return file_raw;
}
-#endif /* CONFIG_CHECKPOINT_RESTORE */
+#endif /* CONFIG_KCMP_SYSCALL */
/**
* Adds a new entry to the tail of the list in a lockless way, i.e.
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index 8f000fada5a4..aa799295e373 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -18,9 +18,7 @@ struct file;
#ifdef CONFIG_EPOLL
-#ifdef CONFIG_CHECKPOINT_RESTORE
struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long toff);
-#endif
/* Used to initialize the epoll bits inside the "struct file" */
static inline void eventpoll_init_file(struct file *file)
diff --git a/init/Kconfig b/init/Kconfig
index 0498af567f70..95e9486d4217 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1158,9 +1158,20 @@ config NET_NS
endif # NAMESPACES
+config KCMP_SYSCALL
+ bool "kcmp system call"
+ help
+ Enable the kcmp system call, which allows one to determine
+ whether to tasks share various kernel resources, for example
+ whether they share address space, or if two file descriptors
+ refer to the same open file description.
+
+ If unsure, say N.
+
config CHECKPOINT_RESTORE
bool "Checkpoint/restore support"
select PROC_CHILDREN
+ select KCMP_SYSCALL
default n
help
Enables additional kernel features in a sake of checkpoint/restore.
diff --git a/kernel/Makefile b/kernel/Makefile
index f3218bc5ec69..3daedba2146a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -49,7 +49,7 @@ obj-y += rcu/
obj-y += livepatch/
obj-y += dma/
-obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o
+obj-$(CONFIG_KCMP_SYSCALL) += kcmp.o
obj-$(CONFIG_FREEZER) += freezer.o
obj-$(CONFIG_PROFILING) += profile.o
obj-$(CONFIG_STACKTRACE) += stacktrace.o
--
2.23.0
