[PATCH v3 bpf-next 0/4] introduce bpf_iter for task_vma

[PATCH v3 bpf-next 0/4] introduce bpf_iter for task_vma

[Song Liu]

This set introduces bpf_iter for task_vma, which can be used to generate
information similar to /proc/pid/maps. Patch 4/4 adds an example that
mimics /proc/pid/maps.

Current /proc/<pid>/maps and /proc/<pid>/smaps provide information of
vma's of a process. However, these information are not flexible enough to
cover all use cases. For example, if a vma cover mixed 2MB pages and 4kB
pages (x86_64), there is no easy way to tell which address ranges are
backed by 2MB pages. task_vma solves the problem by enabling the user to
generate customize information based on the vma (and vma->vm_mm,
vma->vm_file, etc.).

Changes v2 => v3:
  1. Rewrite 1/4 so that we hold mmap_lock while calling BPF program. This
     enables the BPF program to access the real vma with BTF. (Alexei)
  2. Fix the logic when the control is returned to user space. (Yonghong)
  3. Revise commit log and cover letter. (Yonghong)

Changes v1 => v2:
  1. Small fixes in task_iter.c and the selftests. (Yonghong)

Song Liu (4):
  bpf: introduce task_vma bpf_iter
  bpf: allow bpf_d_path in sleepable bpf_iter program
  libbpf: introduce section "iter.s/" for sleepable bpf_iter program
  selftests/bpf: add test for bpf_iter_task_vma

 kernel/bpf/task_iter.c                        | 212 +++++++++++++++++-
 kernel/trace/bpf_trace.c                      |   5 +
 tools/lib/bpf/libbpf.c                        |   5 +
 .../selftests/bpf/prog_tests/bpf_iter.c       | 114 +++++++++-
 tools/testing/selftests/bpf/progs/bpf_iter.h  |   8 +
 .../selftests/bpf/progs/bpf_iter_task_vma.c   |  58 +++++
 6 files changed, 391 insertions(+), 11 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c

--
2.24.1

[PATCH v3 bpf-next 1/4] bpf: introduce task_vma bpf_iter

[Song Liu]

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.

Current /proc/<pid>/maps and /proc/<pid>/smaps provide information of
vma's of a process. However, these information are not flexible enough to
cover all use cases. For example, if a vma cover mixed 2MB pages and 4kB
pages (x86_64), there is no easy way to tell which address ranges are
backed by 2MB pages. task_vma solves the problem by enabling the user to
generate customize information based on the vma (and vma->vm_mm,
vma->vm_file, etc.).

To access the vma safely in the BPF program, task_vma iterator holds
target mmap_lock while calling the BPF program. If the mmap_lock is
contended, task_vma unlocks mmap_lock between iterations to unblock the
writer(s). This lock contention avoidance mechanism is similar to the one
used in show_smaps_rollup().

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 kernel/bpf/task_iter.c | 211 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 210 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 0458a40edf10a..a1d3c9d230f68 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -304,9 +304,192 @@ 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;
+	u32 tid;
+	unsigned long prev_vm_start;
+	unsigned long prev_vm_end;
+};
+
+enum bpf_task_vma_iter_find_op {
+	task_vma_iter_first_vma,   /* use mm->mmap */
+	task_vma_iter_next_vma,    /* use curr_vma->vm_next */
+	task_vma_iter_find_vma,    /* use find_vma() to find next vma */
+};
+
+static struct vm_area_struct *
+task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
+{
+	struct pid_namespace *ns = info->common.ns;
+	enum bpf_task_vma_iter_find_op op;
+	struct vm_area_struct *curr_vma;
+	struct task_struct *curr_task;
+	u32 curr_tid = info->tid;
+
+	/* If this function returns a non-NULL vma, it holds a reference to
+	 * the task_struct, and holds read lock on vma->mm->mmap_lock.
+	 * If this function returns NULL, it does not hold any reference or
+	 * lock.
+	 */
+again:
+	if (info->task) {
+		curr_task = info->task;
+		curr_vma = info->vma;
+		/* In case of lock contention, drop mmap_lock to unblock
+		 * the writer.
+		 */
+		if (mmap_lock_is_contended(curr_task->mm)) {
+			info->prev_vm_start = curr_vma->vm_start;
+			info->prev_vm_end = curr_vma->vm_end;
+			op = task_vma_iter_find_vma;
+			mmap_read_unlock(curr_task->mm);
+			if (mmap_read_lock_killable(curr_task->mm))
+				goto finish;
+		} else {
+			op = task_vma_iter_next_vma;
+		}
+	} else {
+		curr_task = task_seq_get_next(ns, &curr_tid, true);
+		if (!curr_task) {
+			info->tid = curr_tid + 1;
+			goto finish;
+		}
+
+		if (curr_tid != info->tid) {
+			info->tid = curr_tid;
+			op = task_vma_iter_first_vma;
+		} else {
+			op = task_vma_iter_find_vma;
+		}
+
+		if (!curr_task->mm)
+			goto next_task;
+
+		if (mmap_read_lock_killable(curr_task->mm))
+			goto finish;
+	}
+
+	switch (op) {
+	case task_vma_iter_first_vma:
+		curr_vma = curr_task->mm->mmap;
+		break;
+	case task_vma_iter_next_vma:
+		curr_vma = curr_vma->vm_next;
+		break;
+	case task_vma_iter_find_vma:
+		/* We dropped mmap_lock so it is necessary to use find_vma
+		 * to find the next vma. This is similar to the  mechanism
+		 * in show_smaps_rollup().
+		 */
+		curr_vma = find_vma(curr_task->mm, info->prev_vm_end - 1);
+
+		if (curr_vma && (curr_vma->vm_start == info->prev_vm_start))
+			curr_vma = curr_vma->vm_next;
+		break;
+	}
+	if (!curr_vma) {
+		mmap_read_unlock(curr_task->mm);
+		goto next_task;
+	}
+	info->task = curr_task;
+	info->vma = curr_vma;
+	return curr_vma;
+
+next_task:
+	put_task_struct(curr_task);
+	info->task = NULL;
+	curr_tid++;
+	goto again;
+
+finish:
+	info->task = NULL;
+	info->vma = NULL;
+	return NULL;
+}
+
+static void *task_vma_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+	struct vm_area_struct *vma;
+
+	vma = task_vma_seq_get_next(info);
+	if (vma && *pos == 0)
+		++*pos;
+
+	return vma;
+}
+
+static void *task_vma_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+
+	++*pos;
+	return task_vma_seq_get_next(info);
+}
+
+struct bpf_iter__task_vma {
+	__bpf_md_ptr(struct bpf_iter_meta *, meta);
+	__bpf_md_ptr(struct task_struct *, task);
+	__bpf_md_ptr(struct vm_area_struct *, vma);
+};
+
+DEFINE_BPF_ITER_FUNC(task_vma, struct bpf_iter_meta *meta,
+		     struct task_struct *task, struct vm_area_struct *vma)
+
+static int __task_vma_seq_show(struct seq_file *seq, bool in_stop)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+	struct bpf_iter__task_vma ctx;
+	struct bpf_iter_meta meta;
+	struct bpf_prog *prog;
+
+	meta.seq = seq;
+	prog = bpf_iter_get_info(&meta, in_stop);
+	if (!prog)
+		return 0;
+
+	ctx.meta = &meta;
+	ctx.task = info->task;
+	ctx.vma = info->vma;
+	return bpf_iter_run_prog(prog, &ctx);
+}
+
+static int task_vma_seq_show(struct seq_file *seq, void *v)
+{
+	return __task_vma_seq_show(seq, false);
+}
+
+static void task_vma_seq_stop(struct seq_file *seq, void *v)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+
+	if (!v) {
+		(void)__task_vma_seq_show(seq, true);
+	} else {
+		info->prev_vm_start = info->vma->vm_start;
+		info->prev_vm_end = info->vma->vm_end;
+		mmap_read_unlock(info->task->mm);
+		put_task_struct(info->task);
+		info->task = NULL;
+	}
+}
+
+static const struct seq_operations task_vma_seq_ops = {
+	.start	= task_vma_seq_start,
+	.next	= task_vma_seq_next,
+	.stop	= task_vma_seq_stop,
+	.show	= task_vma_seq_show,
+};
+
 BTF_ID_LIST(btf_task_file_ids)
 BTF_ID(struct, task_struct)
 BTF_ID(struct, file)
+BTF_ID(struct, vm_area_struct)
 
 static const struct bpf_iter_seq_info task_seq_info = {
 	.seq_ops		= &task_seq_ops,
@@ -346,6 +529,26 @@ static struct bpf_iter_reg task_file_reg_info = {
 	.seq_info		= &task_file_seq_info,
 };
 
+static const struct bpf_iter_seq_info task_vma_seq_info = {
+	.seq_ops		= &task_vma_seq_ops,
+	.init_seq_private	= init_seq_pidns,
+	.fini_seq_private	= fini_seq_pidns,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_vma_info),
+};
+
+static struct bpf_iter_reg task_vma_reg_info = {
+	.target			= "task_vma",
+	.feature		= BPF_ITER_RESCHED,
+	.ctx_arg_info_size	= 2,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__task_vma, task),
+		  PTR_TO_BTF_ID_OR_NULL },
+		{ offsetof(struct bpf_iter__task_vma, vma),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+	.seq_info		= &task_vma_seq_info,
+};
+
 static int __init task_iter_init(void)
 {
 	int ret;
@@ -357,6 +560,12 @@ static int __init task_iter_init(void)
 
 	task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
 	task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
-	return bpf_iter_reg_target(&task_file_reg_info);
+	ret =  bpf_iter_reg_target(&task_file_reg_info);
+	if (ret)
+		return ret;
+
+	task_vma_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
+	task_vma_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[2];
+	return bpf_iter_reg_target(&task_vma_reg_info);
 }
 late_initcall(task_iter_init);
-- 
2.24.1

Re: [PATCH v3 bpf-next 1/4] bpf: introduce task_vma bpf_iter

[Yonghong Song]

On 1/6/21 8:17 PM, Song Liu wrote:
> 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.
> 
> Current /proc/<pid>/maps and /proc/<pid>/smaps provide information of
> vma's of a process. However, these information are not flexible enough to
> cover all use cases. For example, if a vma cover mixed 2MB pages and 4kB
> pages (x86_64), there is no easy way to tell which address ranges are
> backed by 2MB pages. task_vma solves the problem by enabling the user to
> generate customize information based on the vma (and vma->vm_mm,
> vma->vm_file, etc.).
> 
> To access the vma safely in the BPF program, task_vma iterator holds
> target mmap_lock while calling the BPF program. If the mmap_lock is
> contended, task_vma unlocks mmap_lock between iterations to unblock the
> writer(s). This lock contention avoidance mechanism is similar to the one
> used in show_smaps_rollup().
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>   kernel/bpf/task_iter.c | 211 ++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 210 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index 0458a40edf10a..a1d3c9d230f68 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -304,9 +304,192 @@ 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;
> +	u32 tid;
> +	unsigned long prev_vm_start;
> +	unsigned long prev_vm_end;
> +};
> +
> +enum bpf_task_vma_iter_find_op {
> +	task_vma_iter_first_vma,   /* use mm->mmap */
> +	task_vma_iter_next_vma,    /* use curr_vma->vm_next */
> +	task_vma_iter_find_vma,    /* use find_vma() to find next vma */
> +};
> +
> +static struct vm_area_struct *
> +task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
> +{
> +	struct pid_namespace *ns = info->common.ns;
> +	enum bpf_task_vma_iter_find_op op;
> +	struct vm_area_struct *curr_vma;
> +	struct task_struct *curr_task;
> +	u32 curr_tid = info->tid;
> +
> +	/* If this function returns a non-NULL vma, it holds a reference to
> +	 * the task_struct, and holds read lock on vma->mm->mmap_lock.
> +	 * If this function returns NULL, it does not hold any reference or
> +	 * lock.
> +	 */
> +again:

We can move label "again" to below right before "curr_task = 
task_seq_get_next()" since "goto again" always having info->task == NULL.

> +	if (info->task) {
> +		curr_task = info->task;
> +		curr_vma = info->vma;
> +		/* In case of lock contention, drop mmap_lock to unblock
> +		 * the writer.
> +		 */
> +		if (mmap_lock_is_contended(curr_task->mm)) {
> +			info->prev_vm_start = curr_vma->vm_start;
> +			info->prev_vm_end = curr_vma->vm_end;
> +			op = task_vma_iter_find_vma;
> +			mmap_read_unlock(curr_task->mm);
> +			if (mmap_read_lock_killable(curr_task->mm))

Could you explain when mmap_read_lock_killable() may fail?
What I try to find is if mmap_read_lock_killable() fails, we should
abort iterating or we may request user to try again (if user buffer
is not filled anything).

> +				goto finish;
> +		} else {
> +			op = task_vma_iter_next_vma;
> +		}
> +	} else {
> +		curr_task = task_seq_get_next(ns, &curr_tid, true);
> +		if (!curr_task) {
> +			info->tid = curr_tid + 1;
> +			goto finish;
> +		}
> +
> +		if (curr_tid != info->tid) {
> +			info->tid = curr_tid;
> +			op = task_vma_iter_first_vma;
> +		} else {
> +			op = task_vma_iter_find_vma;
> +		}
> +
> +		if (!curr_task->mm)
> +			goto next_task;
> +
> +		if (mmap_read_lock_killable(curr_task->mm))
> +			goto finish;
> +	}
> +
> +	switch (op) {
> +	case task_vma_iter_first_vma:
> +		curr_vma = curr_task->mm->mmap;
> +		break;
> +	case task_vma_iter_next_vma:
> +		curr_vma = curr_vma->vm_next;
> +		break;
> +	case task_vma_iter_find_vma:
> +		/* We dropped mmap_lock so it is necessary to use find_vma
> +		 * to find the next vma. This is similar to the  mechanism
> +		 * in show_smaps_rollup().
> +		 */
> +		curr_vma = find_vma(curr_task->mm, info->prev_vm_end - 1);
> +
> +		if (curr_vma && (curr_vma->vm_start == info->prev_vm_start))
> +			curr_vma = curr_vma->vm_next;
> +		break;
> +	}
> +	if (!curr_vma) {
> +		mmap_read_unlock(curr_task->mm);
> +		goto next_task;
> +	}
> +	info->task = curr_task;
> +	info->vma = curr_vma;
> +	return curr_vma;
> +
> +next_task:
> +	put_task_struct(curr_task);
> +	info->task = NULL;
> +	curr_tid++;
> +	goto again;
> +
> +finish:
> +	info->task = NULL;
> +	info->vma = NULL;
> +	return NULL;
> +}
> +
> +static void *task_vma_seq_start(struct seq_file *seq, loff_t *pos)
> +{
> +	struct bpf_iter_seq_task_vma_info *info = seq->private;
> +	struct vm_area_struct *vma;
> +
> +	vma = task_vma_seq_get_next(info);
> +	if (vma && *pos == 0)
> +		++*pos;
> +
> +	return vma;
> +}
> +
> +static void *task_vma_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> +{
> +	struct bpf_iter_seq_task_vma_info *info = seq->private;
> +
> +	++*pos;
> +	return task_vma_seq_get_next(info);
> +}
> +
> +struct bpf_iter__task_vma {
> +	__bpf_md_ptr(struct bpf_iter_meta *, meta);
> +	__bpf_md_ptr(struct task_struct *, task);
> +	__bpf_md_ptr(struct vm_area_struct *, vma);
> +};
> +
> +DEFINE_BPF_ITER_FUNC(task_vma, struct bpf_iter_meta *meta,
> +		     struct task_struct *task, struct vm_area_struct *vma)
> +
> +static int __task_vma_seq_show(struct seq_file *seq, bool in_stop)
> +{
> +	struct bpf_iter_seq_task_vma_info *info = seq->private;
> +	struct bpf_iter__task_vma ctx;
> +	struct bpf_iter_meta meta;
> +	struct bpf_prog *prog;
> +
> +	meta.seq = seq;
> +	prog = bpf_iter_get_info(&meta, in_stop);
> +	if (!prog)
> +		return 0;
> +
> +	ctx.meta = &meta;
> +	ctx.task = info->task;
> +	ctx.vma = info->vma;
> +	return bpf_iter_run_prog(prog, &ctx);
> +}
> +
> +static int task_vma_seq_show(struct seq_file *seq, void *v)
> +{
> +	return __task_vma_seq_show(seq, false);
> +}
> +
> +static void task_vma_seq_stop(struct seq_file *seq, void *v)
> +{
> +	struct bpf_iter_seq_task_vma_info *info = seq->private;
> +
> +	if (!v) {
> +		(void)__task_vma_seq_show(seq, true);
> +	} else {
> +		info->prev_vm_start = info->vma->vm_start;
> +		info->prev_vm_end = info->vma->vm_end;

This change, together with task_vma_iter_find_vma action,
is not correct.

What we typically have is info->vma->vm_start/info->vma->vm_end
is the next show but since there is no room for that we will
delay until user space processed buffer and come back.
So here, it is not prev_vm_start/end as it has not been
displayed.

Maybe you can separate task_vma_iter_find_vma into two?
task_vma_iter_find_vma and task_vma_iter_find_vma_next.
(task_vma_iter_find_vma_next carriers the action with
what you have now for task_vma_iter_find_vma).

In the above task_vma_seq_get_next(), if info->task != NULL,
you will use task_vma_iter_find_vma_next (the one after previous
vm_start/end), if info->task == NULL, which means back from user
space, not going to next vma if there is an exact match.

> +		mmap_read_unlock(info->task->mm);
> +		put_task_struct(info->task);
> +		info->task = NULL;
> +	}
> +}
> +
> +static const struct seq_operations task_vma_seq_ops = {
> +	.start	= task_vma_seq_start,
> +	.next	= task_vma_seq_next,
> +	.stop	= task_vma_seq_stop,
> +	.show	= task_vma_seq_show,
> +};
> +
>   BTF_ID_LIST(btf_task_file_ids)
>   BTF_ID(struct, task_struct)
>   BTF_ID(struct, file)
> +BTF_ID(struct, vm_area_struct)
>   
>   static const struct bpf_iter_seq_info task_seq_info = {
>   	.seq_ops		= &task_seq_ops,
> @@ -346,6 +529,26 @@ static struct bpf_iter_reg task_file_reg_info = {
>   	.seq_info		= &task_file_seq_info,
>   };
>   
> +static const struct bpf_iter_seq_info task_vma_seq_info = {
> +	.seq_ops		= &task_vma_seq_ops,
> +	.init_seq_private	= init_seq_pidns,
> +	.fini_seq_private	= fini_seq_pidns,
> +	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_vma_info),
> +};
> +
> +static struct bpf_iter_reg task_vma_reg_info = {
> +	.target			= "task_vma",
> +	.feature		= BPF_ITER_RESCHED,
> +	.ctx_arg_info_size	= 2,
> +	.ctx_arg_info		= {
> +		{ offsetof(struct bpf_iter__task_vma, task),
> +		  PTR_TO_BTF_ID_OR_NULL },
> +		{ offsetof(struct bpf_iter__task_vma, vma),
> +		  PTR_TO_BTF_ID_OR_NULL },
> +	},
> +	.seq_info		= &task_vma_seq_info,
> +};
> +
>   static int __init task_iter_init(void)
>   {
>   	int ret;
> @@ -357,6 +560,12 @@ static int __init task_iter_init(void)
>   
>   	task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
>   	task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
> -	return bpf_iter_reg_target(&task_file_reg_info);
> +	ret =  bpf_iter_reg_target(&task_file_reg_info);
> +	if (ret)
> +		return ret;
> +
> +	task_vma_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
> +	task_vma_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[2];
> +	return bpf_iter_reg_target(&task_vma_reg_info);
>   }
>   late_initcall(task_iter_init);
> 

[PATCH v3 bpf-next 4/4] selftests/bpf: add test for bpf_iter_task_vma

[Song Liu]

The test dumps information similar to /proc/pid/maps. The first line of
the output is compared against the /proc file to make sure they match.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       | 114 ++++++++++++++++--
 tools/testing/selftests/bpf/progs/bpf_iter.h  |   8 ++
 .../selftests/bpf/progs/bpf_iter_task_vma.c   |  58 +++++++++
 3 files changed, 170 insertions(+), 10 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 0e586368948dd..9e8027685e859 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -7,6 +7,7 @@
 #include "bpf_iter_task.skel.h"
 #include "bpf_iter_task_stack.skel.h"
 #include "bpf_iter_task_file.skel.h"
+#include "bpf_iter_task_vma.skel.h"
 #include "bpf_iter_task_btf.skel.h"
 #include "bpf_iter_tcp4.skel.h"
 #include "bpf_iter_tcp6.skel.h"
@@ -64,6 +65,22 @@ static void do_dummy_read(struct bpf_program *prog)
 	bpf_link__destroy(link);
 }
 
+static int read_fd_into_buffer(int fd, char *buf, int size)
+{
+	int bufleft = size;
+	int len;
+
+	do {
+		len = read(fd, buf, bufleft);
+		if (len > 0) {
+			buf += len;
+			bufleft -= len;
+		}
+	} while (len > 0);
+
+	return len < 0 ? len : size - bufleft;
+}
+
 static void test_ipv6_route(void)
 {
 	struct bpf_iter_ipv6_route *skel;
@@ -177,7 +194,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
 {
 	struct bpf_program *prog = skel->progs.dump_task_struct;
 	struct bpf_iter_task_btf__bss *bss = skel->bss;
-	int iter_fd = -1, len = 0, bufleft = TASKBUFSZ;
+	int iter_fd = -1, err;
 	struct bpf_link *link;
 	char *buf = taskbuf;
 	int ret = 0;
@@ -190,14 +207,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
 	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
 		goto free_link;
 
-	do {
-		len = read(iter_fd, buf, bufleft);
-		if (len > 0) {
-			buf += len;
-			bufleft -= len;
-		}
-	} while (len > 0);
-
+	err = read_fd_into_buffer(iter_fd, buf, TASKBUFSZ);
 	if (bss->skip) {
 		printf("%s:SKIP:no __builtin_btf_type_id\n", __func__);
 		ret = 1;
@@ -205,7 +215,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
 		goto free_link;
 	}
 
-	if (CHECK(len < 0, "read", "read failed: %s\n", strerror(errno)))
+	if (CHECK(err < 0, "read", "read failed: %s\n", strerror(errno)))
 		goto free_link;
 
 	CHECK(strstr(taskbuf, "(struct task_struct)") == NULL,
@@ -1133,6 +1143,88 @@ static void test_buf_neg_offset(void)
 		bpf_iter_test_kern6__destroy(skel);
 }
 
+#define CMP_BUFFER_SIZE 1024
+static char task_vma_output[CMP_BUFFER_SIZE];
+static char proc_maps_output[CMP_BUFFER_SIZE];
+
+/* remove \0 and \t from str, and only keep the first line */
+static void str_strip_first_line(char *str)
+{
+	char *dst = str, *src = str;
+
+	do {
+		if (*src == ' ' || *src == '\t')
+			src++;
+		else
+			*(dst++) = *(src++);
+
+	} while (*src != '\0' && *src != '\n');
+
+	*dst = '\0';
+}
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+static void test_task_vma(void)
+{
+	int err, iter_fd = -1, proc_maps_fd = -1;
+	struct bpf_iter_task_vma *skel;
+	int len, read_size = 4;
+	char maps_path[64];
+
+	skel = bpf_iter_task_vma__open();
+	if (CHECK(!skel, "bpf_iter_task_vma__open", "skeleton open failed\n"))
+		return;
+
+	skel->bss->pid = getpid();
+
+	err = bpf_iter_task_vma__load(skel);
+	if (CHECK(err, "bpf_iter_task_vma__load", "skeleton load failed\n"))
+		goto out;
+
+	skel->links.proc_maps = bpf_program__attach_iter(
+		skel->progs.proc_maps, NULL);
+
+	if (CHECK(IS_ERR(skel->links.proc_maps), "bpf_program__attach_iter",
+		  "attach iterator failed\n"))
+		goto out;
+
+	/* read CMP_BUFFER_SIZE (1kB) from bpf_iter */
+	iter_fd = bpf_iter_create(bpf_link__fd(skel->links.proc_maps));
+	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
+		goto out;
+
+	/* read in small chunks to trigger seq_file corner cases */
+	len = 0;
+	while (len < CMP_BUFFER_SIZE) {
+		err = read_fd_into_buffer(iter_fd, task_vma_output + len,
+					  min(read_size, CMP_BUFFER_SIZE - len));
+		if (CHECK(err < 0, "read_iter_fd", "read_iter_fd failed\n"))
+			goto out;
+		len += err;
+	}
+
+	/* read CMP_BUFFER_SIZE (1kB) from /proc/pid/maps */
+	snprintf(maps_path, 64, "/proc/%u/maps", skel->bss->pid);
+	proc_maps_fd = open(maps_path, O_RDONLY);
+	if (CHECK(proc_maps_fd < 0, "open_proc_maps", "open_proc_maps failed\n"))
+		goto out;
+	err = read_fd_into_buffer(proc_maps_fd, proc_maps_output, CMP_BUFFER_SIZE);
+	if (CHECK(err < 0, "read_prog_maps_fd", "read_prog_maps_fd failed\n"))
+		goto out;
+
+	/* strip and compare the first line of the two files */
+	str_strip_first_line(task_vma_output);
+	str_strip_first_line(proc_maps_output);
+
+	CHECK(strcmp(task_vma_output, proc_maps_output), "compare_output",
+	      "found mismatch\n");
+out:
+	close(proc_maps_fd);
+	close(iter_fd);
+	bpf_iter_task_vma__destroy(skel);
+}
+
 void test_bpf_iter(void)
 {
 	if (test__start_subtest("btf_id_or_null"))
@@ -1149,6 +1241,8 @@ void test_bpf_iter(void)
 		test_task_stack();
 	if (test__start_subtest("task_file"))
 		test_task_file();
+	if (test__start_subtest("task_vma"))
+		test_task_vma();
 	if (test__start_subtest("task_btf"))
 		test_task_btf();
 	if (test__start_subtest("tcp4"))
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter.h b/tools/testing/selftests/bpf/progs/bpf_iter.h
index 6a1255465fd6d..3d83b185c4bcb 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter.h
+++ b/tools/testing/selftests/bpf/progs/bpf_iter.h
@@ -7,6 +7,7 @@
 #define bpf_iter__netlink bpf_iter__netlink___not_used
 #define bpf_iter__task bpf_iter__task___not_used
 #define bpf_iter__task_file bpf_iter__task_file___not_used
+#define bpf_iter__task_vma bpf_iter__task_vma___not_used
 #define bpf_iter__tcp bpf_iter__tcp___not_used
 #define tcp6_sock tcp6_sock___not_used
 #define bpf_iter__udp bpf_iter__udp___not_used
@@ -26,6 +27,7 @@
 #undef bpf_iter__netlink
 #undef bpf_iter__task
 #undef bpf_iter__task_file
+#undef bpf_iter__task_vma
 #undef bpf_iter__tcp
 #undef tcp6_sock
 #undef bpf_iter__udp
@@ -67,6 +69,12 @@ struct bpf_iter__task_file {
 	struct file *file;
 } __attribute__((preserve_access_index));
 
+struct bpf_iter__task_vma {
+	struct bpf_iter_meta *meta;
+	struct task_struct *task;
+	struct vm_area_struct *vma;
+} __attribute__((preserve_access_index));
+
 struct bpf_iter__bpf_map {
 	struct bpf_iter_meta *meta;
 	struct bpf_map *map;
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
new file mode 100644
index 0000000000000..d789e32cdb16c
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "bpf_iter.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+/* Copied from mm.h */
+#define VM_READ		0x00000001
+#define VM_WRITE	0x00000002
+#define VM_EXEC		0x00000004
+#define VM_MAYSHARE	0x00000080
+
+/* Copied from kdev_t.h */
+#define MINORBITS	20
+#define MINORMASK	((1U << MINORBITS) - 1)
+#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
+#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
+
+#define D_PATH_BUF_SIZE 1024
+char d_path_buf[D_PATH_BUF_SIZE] = {};
+__u32 pid = 0;
+
+SEC("iter.s/task_vma") int proc_maps(struct bpf_iter__task_vma *ctx)
+{
+	struct vm_area_struct *vma = ctx->vma;
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	struct file *file;
+	char perm_str[] = "----";
+
+	if (task == (void *)0 || vma == (void *)0)
+		return 0;
+
+	file = vma->vm_file;
+	if (task->tgid != pid)
+		return 0;
+	perm_str[0] = (vma->vm_flags & VM_READ) ? 'r' : '-';
+	perm_str[1] = (vma->vm_flags & VM_WRITE) ? 'w' : '-';
+	perm_str[2] = (vma->vm_flags & VM_EXEC) ? 'x' : '-';
+	perm_str[3] = (vma->vm_flags & VM_MAYSHARE) ? 's' : 'p';
+	BPF_SEQ_PRINTF(seq, "%08llx-%08llx %s ", vma->vm_start, vma->vm_end, perm_str);
+
+	if (file) {
+		__u32 dev = file->f_inode->i_sb->s_dev;
+
+		bpf_d_path(&file->f_path, d_path_buf, D_PATH_BUF_SIZE);
+
+		BPF_SEQ_PRINTF(seq, "%08llx ", vma->vm_pgoff << 12);
+		BPF_SEQ_PRINTF(seq, "%02x:%02x %u", MAJOR(dev), MINOR(dev),
+			       file->f_inode->i_ino);
+		BPF_SEQ_PRINTF(seq, "\t%s\n", d_path_buf);
+	} else {
+		BPF_SEQ_PRINTF(seq, "%08llx 00:00 0\n", 0ULL);
+	}
+	return 0;
+}
-- 
2.24.1

Re: [PATCH v3 bpf-next 2/4] bpf: allow bpf_d_path in sleepable bpf_iter program

[KP Singh]

On Thu, Jan 7, 2021 at 5:23 AM Song Liu <songliubraving@fb.com> wrote:
>
> task_file and task_vma iter programs have access to file->f_path. Enable
> bpf_d_path to print paths of these file.
>
> bpf_iter programs are generally called in sleepable context. However, it
> is still necessary to diffientiate sleepable and non-sleepable bpf_iter
> programs: sleepable programs have access to bpf_d_path; non-sleepable
> programs have access to bpf_spin_lock.
>
> Acked-by: Yonghong Song <yhs@fb.com>
> Signed-off-by: Song Liu <songliubraving@fb.com>

Acked-by: KP Singh <kpsingh@kernel.org>