[PATCH] commands: sync: add new command to flush cached writes

[Sascha Hauer]

On Tue, Jul 30, 2024 at 09:16:32AM +0200, Ahmad Fatoum wrote:
> In barebox, the dirty block cache for a given device is flushed when
> closing all file descriptors to it, a cached block needs to be evicted
> due to pressure or when barebox shuts down.
> 
> There are valid uses to do it explicitly however:
> 
>   - When benchmarking write speed to a block device
>   - Before forced resets, because a regular reset would run shutdown
>     code that should be omitted.
> 
> Add a sync command that does this. Unlike the userspace variant, we
> don't both to implement a argument-less sync that's global. Users are
> supposed to flush the files they are actually interested in, e.g.:
> 
>   sync /dev/mmc2.0
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>

I'll drop this one in favor for the same patch included in your mmc
erase support series.

Sascha

> ---
>  commands/Kconfig  | 14 ++++++++++++++
>  commands/Makefile |  1 +
>  commands/sync.c   | 42 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 57 insertions(+)
>  create mode 100644 commands/sync.c
> 
> diff --git a/commands/Kconfig b/commands/Kconfig
> index 5b512f1bbac7..a8b7037618cc 100644
> --- a/commands/Kconfig
> +++ b/commands/Kconfig
> @@ -1871,6 +1871,20 @@ config CMD_DETECT
>  		  -e	bail out if one device fails to detect
>  		  -a	detect all devices
>  
> +config CMD_SYNC
> +	tristate
> +	prompt "sync"
> +	help
> +	  sync - flush cached writes
> +
> +	  Usage: sync DEVICE
> +
> +	  Synchronize cached writes to persistent storage of DEVICE
> +	  immediately instead of waiting for block device to be closed,
> +	  cache eviction or the regular barebox exit.
> +
> +	  This command is mainly useful for benchmarking.
> +
>  config CMD_FLASH
>  	tristate
>  	prompt "erase, protect and unprotect"
> diff --git a/commands/Makefile b/commands/Makefile
> index 4ca7ba7eb609..a9dbead4389f 100644
> --- a/commands/Makefile
> +++ b/commands/Makefile
> @@ -41,6 +41,7 @@ obj-$(CONFIG_CMD_REGINFO)	+= reginfo.o
>  obj-$(CONFIG_CMD_CRC)		+= crc.o
>  obj-$(CONFIG_CMD_CLEAR)		+= clear.o
>  obj-$(CONFIG_CMD_TEST)		+= test.o
> +obj-$(CONFIG_CMD_SYNC)		+= sync.o
>  obj-$(CONFIG_CMD_FLASH)		+= flash.o
>  obj-$(CONFIG_CMD_MEMINFO)	+= meminfo.o
>  obj-$(CONFIG_CMD_TIMEOUT)	+= timeout.o
> diff --git a/commands/sync.c b/commands/sync.c
> new file mode 100644
> index 000000000000..6add67cd0876
> --- /dev/null
> +++ b/commands/sync.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +/* sync - flushing support */
> +
> +#include <common.h>
> +#include <command.h>
> +#include <fcntl.h>
> +#include <fs.h>
> +
> +static int do_sync(int argc, char *argv[])
> +{
> +	int ret, fd;
> +
> +	if (argc != 2)
> +		return COMMAND_ERROR_USAGE;
> +
> +	fd = open(argv[1], O_WRONLY);
> +	if (fd < 0) {
> +		printf("open %s: %m\n", argv[1]);
> +		return 1;
> +	}
> +
> +	ret = flush(fd);
> +
> +	close(fd);
> +
> +	return ret;
> +}
> +
> +BAREBOX_CMD_HELP_START(sync)
> +BAREBOX_CMD_HELP_TEXT("Synchronize cached writes to persistent storage of DEVICE")
> +BAREBOX_CMD_HELP_TEXT("immediately instead of waiting for block device to be closed,")
> +BAREBOX_CMD_HELP_TEXT("cache eviction or the regular barebox exit.")
> +BAREBOX_CMD_HELP_END
> +
> +BAREBOX_CMD_START(sync)
> +	.cmd		= do_sync,
> +	BAREBOX_CMD_DESC("flush cached writes")
> +	BAREBOX_CMD_OPTS("DEVICE")
> +	BAREBOX_CMD_GROUP(CMD_GRP_HWMANIP)
> +	BAREBOX_CMD_HELP(cmd_sync_help)
> +BAREBOX_CMD_END
> -- 
> 2.39.2
> 
> 
> 

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