Dear TigerLiu@via-alliance.com,
In message FE7ADED5C2218B4786C09CD97DC4C49FDAE8CF@exchbj02.viatech.com.bj you wrote:
I want to know the size limit for a single env variable.
In theory the size of the variable is only limited by the free room in the envrionment (the size of which you configure in your board config file).
I have reviewed the code:
It seems the size limit for a single env variable is 1M bytes, right?
#define MAX_ENV_SIZE (1 << 20) /* 1 MiB */
(in common/cmd_nvedit.c)
Wrong. This limit applies only for the "env import" code - it is a (theoretical) limit for the size of an environment blob that we can import.
Note however, that you will hit other limits much earlier:
- Typically, the environment size (i. e. the room for all variables) is a few KiB; 8...16 KiB is a reasonable size which fits even very complex situations.
- To be able to manipulate the environment, you need to be able to actually enter the commands, i. e. you are limited by the console I/O Buffer Size (CONFIG_SYS_CBSIZE) and also by the print buffer size (CONFIG_SYS_PBSIZE). In many cases, these are set to 256... 1024 bytes - only 3 boards use more (2 x 2 KiB, 1 x 4 KiB).
In general, your question makes me fear you are considering to do something seriously wrong. The environment is not a sutiable means to store any larger blobs of data. It is intended for a few (maybe some ten) variables, and theier values should be not longer than typical commands you might use on the command line - say, some 20...60 characters.
When you find that your used environment size significantly exceeds 2...4 KiB, you should lean back and review what you are doing, because most probably you are doing something pretty much wrong.
What exactly was your reason to worry about the maximum size for env vars?
Best regards,
Wolfgang Denk