Implementing shell commands

Command definition

Commands are added to U-Boot by creating a new command structure. This is done by first including command.h, then using the U_BOOT_CMD() or the U_BOOT_CMD_COMPLETE macro to fill in a struct cmd_tbl structure.

U_BOOT_CMD(name, maxargs, repeatable, command, "usage", "help")
U_BOOT_CMD_COMPLETE(name, maxargs, repeatable, command, "usage, "help", comp)

name: The name of the command. This is not a string.
maxargs: The maximum number of arguments this function takes including the command itself.
repeatable: Either 0 or 1 to indicate if autorepeat is allowed.
command: Pointer to the command function. This is the function that is called when the command is issued.
usage: Short description. This is a string.
help: Long description. This is a string. The long description is only available if CONFIG_SYS_LONGHELP is defined.
comp: Pointer to the completion function. May be NULL. This function is called if the user hits the TAB key while entering the command arguments to complete the entry. Command completion is only available if CONFIG_AUTO_COMPLETE is defined.

Sub-command definition

Likewise an array of struct cmd_tbl holding sub-commands can be created using either of the following macros:

U_BOOT_CMD_MKENT(name, maxargs, repeatable, command, "usage", "help")
U_BOOT_CMD_MKENTCOMPLETE(name, maxargs, repeatable, command, "usage, "help", comp)

This table has to be evaluated in the command function of the main command, e.g.

static struct cmd_tbl cmd_sub[] = {
    U_BOOT_CMD_MKENT(foo, CONFIG_SYS_MAXARGS, 1, do_foo, "", ""),
    U_BOOT_CMD_MKENT(bar, CONFIG_SYS_MAXARGS, 1, do_bar, "", ""),
};

static int do_cmd(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
{
    struct cmd_tbl *cp;

    if (argc < 2)
            return CMD_RET_USAGE;

    /* drop sub-command argument */
    argc--;
    argv++;

    cp = find_cmd_tbl(argv[0], cmd_ut_sub, ARRAY_SIZE(cmd_sub));

    if (cp)
        return cp->cmd(cmdtp, flag, argc, argv);

    return CMD_RET_USAGE;
}

Command function

The command function pointer has to be of type

int (*cmd)(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[]);

cmdtp

Table entry describing the command (see above).

flag

A bitmap which may contain the following bits

CMD_FLAG_REPEAT - The last command is repeated.
CMD_FLAG_BOOTD - The command is called by the bootd command.
CMD_FLAG_ENV - The command is called by the run command.

argc

Number of arguments including the command.

argv

Arguments.

Allowable return value are:

CMD_RET_SUCCESS: The command was successfully executed.
CMD_RET_FAILURE: The command failed.
CMD_RET_USAGE: The command was called with invalid parameters. This value leads to the display of the usage string.

Completion function

The completion function pointer has to be of type

int (*complete)(int argc, char *const argv[], char last_char,
                int maxv, char *cmdv[]);

argc: Number of arguments including the command.
argv: Arguments.
last_char: The last character in the command line buffer.
maxv: Maximum number of possible completions that may be returned by the function.
cmdv: Used to return possible values for the last argument. The last possible completion must be followed by NULL.

The function returns the number of possible completions (without the terminating NULL value).

Behind the scene

The structure created is named with a special prefix and placed by the linker in a special section using the linker lists mechanism (see include/linker_lists.h)

This makes it possible for the final link to extract all commands compiled into any object code and construct a static array so the command array can be iterated over using the linker lists macros.

The linker lists feature ensures that the linker does not discard these symbols when linking full U-Boot even though they are not referenced in the source code as such.

If a new board is defined do not forget to define the command section by writing in u-boot.lds ($(srctree)/board/boardname/u-boot.lds) these 3 lines:

__u_boot_list : {
    KEEP(*(SORT(__u_boot_list*)));
}

Writing tests

All new commands should have tests. Tests for existing commands are very welcome.

It is fairly easy to write a test for a command. Enable it in sandbox, and then add code that runs the command and checks the output.

Here is an example:

/* Test 'acpi items' command */
static int dm_test_acpi_cmd_items(struct unit_test_state *uts)
{
    struct acpi_ctx ctx;
    void *buf;

    buf = malloc(BUF_SIZE);
    ut_assertnonnull(buf);

    ctx.current = buf;
    ut_assertok(acpi_fill_ssdt(&ctx));
    console_record_reset();
    run_command("acpi items", 0);
    ut_assert_nextline("dev 'acpi-test', type 1, size 2");
    ut_assert_nextline("dev 'acpi-test2', type 1, size 2");
    ut_assert_console_end();

    ctx.current = buf;
    ut_assertok(acpi_inject_dsdt(&ctx));
    console_record_reset();
    run_command("acpi items", 0);
    ut_assert_nextline("dev 'acpi-test', type 2, size 2");
    ut_assert_nextline("dev 'acpi-test2', type 2, size 2");
    ut_assert_console_end();

    console_record_reset();
    run_command("acpi items -d", 0);
    ut_assert_nextline("dev 'acpi-test', type 2, size 2");
    ut_assert_nextlines_are_dump(2);
    ut_assert_nextline("%s", "");
    ut_assert_nextline("dev 'acpi-test2', type 2, size 2");
    ut_assert_nextlines_are_dump(2);
    ut_assert_nextline("%s", "");
    ut_assert_console_end();

    return 0;
}
DM_TEST(dm_test_acpi_cmd_items, UT_TESTF_SCAN_PDATA | UT_TESTF_SCAN_FDT);