Re: [PATCH bpf-next 1/4] bpf: introduce task_vma bpf_iter

Introduce task_vma bpf_iter to print memory information of a process. It
can be used to print customized information similar to /proc/<pid>/maps.

task_vma iterator releases mmap_lock before calling the BPF program.
Therefore, we cannot pass vm_area_struct directly to the BPF program. A
new __vm_area_struct is introduced to keep key information of a vma. On
each iteration, task_vma gathers information in __vm_area_struct and
passes it to the BPF program.

If the vma maps to a file, task_vma also holds a reference to the file
while calling the BPF program.

Signed-off-by: Song Liu <redacted>
---
  include/linux/bpf.h      |   2 +-
  include/uapi/linux/bpf.h |   7 ++
  kernel/bpf/task_iter.c   | 193 ++++++++++++++++++++++++++++++++++++++-
  3 files changed, 200 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 07cb5d15e7439..49dd1e29c8118 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1325,7 +1325,7 @@ enum bpf_iter_feature {
  	BPF_ITER_RESCHED	= BIT(0),
  };
  
-#define BPF_ITER_CTX_ARG_MAX 2
+#define BPF_ITER_CTX_ARG_MAX 3
  struct bpf_iter_reg {
  	const char *target;
  	bpf_iter_attach_target_t attach_target;

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 30b477a264827..c2db8a1d0cbd2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -5151,4 +5151,11 @@ enum {
  	BTF_F_ZERO	=	(1ULL << 3),
  };
  
+struct __vm_area_struct {
+	__u64 start;
+	__u64 end;
+	__u64 flags;
+	__u64 pgoff;
+};

+
  #endif /* _UAPI__LINUX_BPF_H__ */

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 0458a40edf10a..30e5475d0831e 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c

@@ -304,9 +304,171 @@ static const struct seq_operations task_file_seq_ops = {
  	.show	= task_file_seq_show,
  };
  
+struct bpf_iter_seq_task_vma_info {
+	/* The first field must be struct bpf_iter_seq_task_common.
+	 * this is assumed by {init, fini}_seq_pidns() callback functions.
+	 */
+	struct bpf_iter_seq_task_common common;
+	struct task_struct *task;
+	struct __vm_area_struct vma;
+	struct file *file;
+	u32 tid;
+};
+