Re: [PATCH bpf] libbpf: clarify batch lookup semantics

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




On 2/20/24 5:00 PM, Martin Kelly wrote:
The batch lookup APIs copy key memory into out_batch, which is then

The above 'key memory' is not precise. The 'in_batch' and 'out_batch'
intends to be opaque and its size is map specific. So maybe we could
reword the description like below:

The batch lookup and lookup_and_delete APIs have two parameters,
in_batch and out_batch, to facilitate iterative lookup/lookup_and_deletion
operations for supported maps. Except NULL for in_batch at the start
of these two batch operations, both parameters need to point to memory
equal or larger than the respective map size, except for various hashmaps
(hash, percpu_hash, lru_hash, lru_percpu_hash) where the in_batch/out_batch
memory size should be at least 4 bytes.

Please also change your patch subject to
  [PATCH bpf-next] bpf: Clarify batch lookup/lookup_and_delete semantics

supplied in later calls to in_batch. Thus both parameters need to point
to memory large enough to hold a single key (other than an initial NULL
in_batch). For many maps, keys are pointer sized or less, but for larger
maps, it's important to point to a larger block of memory to avoid
memory corruption.

Document these semantics to clarify the API.

Signed-off-by: Martin Kelly <martin.kelly@xxxxxxxxxxxxxxx>
---
  include/uapi/linux/bpf.h |  5 ++++-
  tools/lib/bpf/bpf.h      | 15 ++++++++++-----
  2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d96708380e52..dae613b8778a 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -617,7 +617,10 @@ union bpf_iter_link_info {
   *		to NULL to begin the batched operation. After each subsequent
   *		**BPF_MAP_LOOKUP_BATCH**, the caller should pass the resultant
   *		*out_batch* as the *in_batch* for the next operation to
- *		continue iteration from the current point.
+ *		continue iteration from the current point. Both *in_batch* and
+ *		*out_batch* must point to memory large enough to hold a key,
+ *		except for maps of type **BPF_MAP_TYPE_HASH**, for which batch

Not just BPF_MAP_TYPE_HASH. It should be
BPF_MAP_TYPE_{HASH, PERCPU_HASH, LRU_HASH, LRU_PERCPU_HASH}.
Similar for some changes below.

+ *		parameters must be at least 4 bytes wide regardless of key size.
   *
   *		The *keys* and *values* are output parameters which must point
   *		to memory large enough to hold *count* items based on the key

Please also sync updated include/uapi/linux/bpf.h to tools/include/uapi/linux/bpf.h.

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index ab2570d28aec..c7e918ab0a60 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -190,10 +190,13 @@ LIBBPF_API int bpf_map_delete_batch(int fd, const void *keys,
  /**
   * @brief **bpf_map_lookup_batch()** allows for batch lookup of BPF map elements.
   *
- * The parameter *in_batch* is the address of the first element in the batch to read.
- * *out_batch* is an output parameter that should be passed as *in_batch* to subsequent
- * calls to **bpf_map_lookup_batch()**. NULL can be passed for *in_batch* to indicate
- * that the batched lookup starts from the beginning of the map.
+ * The parameter *in_batch* is the address of the first element in the batch to
+ * read. *out_batch* is an output parameter that should be passed as *in_batch*
+ * to subsequent calls to **bpf_map_lookup_batch()**. NULL can be passed for
+ * *in_batch* to indicate that the batched lookup starts from the beginning of
+ * the map. Both *in_batch* and *out_batch* must point to memory large enough to
+ * hold a single key, except for maps of type **BPF_MAP_TYPE_HASH**, for which
+ * the memory pointed to must be at least 4 bytes wide regardless of key size.
   *
   * The *keys* and *values* are output parameters which must point to memory large enough to
   * hold *count* items based on the key and value size of the map *map_fd*. The *keys*
@@ -226,7 +229,9 @@ LIBBPF_API int bpf_map_lookup_batch(int fd, void *in_batch, void *out_batch,
   *
   * @param fd BPF map file descriptor
   * @param in_batch address of the first element in batch to read, can pass NULL to
- * get address of the first element in *out_batch*
+ * get address of the first element in *out_batch*. If not NULL, must be large
+ * enough to hold a key. For **BPF_MAP_TYPE_HASH**, must be large enough to hold
+ * 4 bytes.
   * @param out_batch output parameter that should be passed to next call as *in_batch*
   * @param keys pointer to an array of *count* keys
   * @param values pointer to an array large enough for *count* values




[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux