BPF Syscall BPF_MAP_LOOKUP_BATCH command
The BPF_MAP_LOOKUP_BATCH command is used to iterate over maps in batches. This can be significantly faster than doing BPF_MAP_GET_NEXT_KEY and BPF_MAP_LOOKUP_ELEM calls.
Note
This command is less widely supported, than the normal single-key lookup command. Check the page of a given map type to check for compatibility.
Return value
This command will return 0 on success or a error number (negative integer) if something went wrong.
Attributes
map_fd
This attribute specifies the file descriptor of the map in which you wish to lookup a value.
in_batch
This attribute is set by userspace. At the start of iteration it should be set to 0/NULL. After the first call, the result of out_batch can me moved to this attribute to get the next batch of keys and values. The value is opaque, the kernel as internally assigned meaning, but userspace should just copy the values without modification.
out_batch
This attribute is set by the kernel during the command exectution. At the start of iteration it should be set to 0/NULL. The kernel will
keys
This attribute is an output with this command unlike with the non-batched lookup command. It holds a pointer to memory where a batch of keys will be written to. The size of this memory is should at least be the key_size attribute of the map you specified with map_fd times the count specified.
values
This attribute holds a pointer to a memory location where the kernel will write the batch of values to. The user should make sure that this memory is at least value_size times count bytes for non-per-CPU maps and value_size * # of logical CPUs * count for per-CPU maps.
For per-CPU maps, the value is a two dimensional array indexed by batch index and then the logical CPU number.
Note
In the case of per-CPU maps, the value_size is rounded up to the nearest multiple of 8 bytes. So a 12-byte value will have 4-bytes of padding between each value.
The kernel will write the value(s) to the memory indicated by this field.
Warning
The kernel may overwrite other neighboring memory if incorrectly sized.
count
This attribute is both an input and output. When calling the command it specifies the maximum amount of keys and values to be retrieved. The kernel will modify the field to reflect the actual count of keys and values that were copied, which might be less than the maximum.
elem_flags
This attribute is a bitmask of flags applied internally for each element lookup.
BPF_F_LOCK
If this flag is set, the command will acquire the spin-lock of the map value we are looking up. If the map contains no spin-lock in its value, -EINVAL will be returned by the command.
flags
This attribute is a bitmask of flags for the batch operation as a whole, there are currently no valid flags defined.