[PATCH v3 8/9] efi/libstub: Add efi_snprintf() to construct wide strings

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

The native EFI character set is UTF-16 (or in practice, UCS-2).
Implement efi_snprintf() to construct UTF-16 strings using printf style
templates. This will be used in a subsequent patch to set the
LoaderDevicePartUUID EFI variable.

Link: https://lore.kernel.org/all/20260903-efi_stub_bli-v2-1-dbf7ba915117@kernel.org/
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/libstub/efistub.h  |  1 +
 drivers/firmware/efi/libstub/vsprintf.c | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 36056c624782..880c1d0c464b 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -1084,6 +1084,7 @@ int efi_vsnprintf(efi_char16_t *buf, size_t size, const char *fmt, va_list ap,
 		  bool crlf);
 
 __printf(1, 2) int efi_printk(char const *fmt, ...);
+__printf(3, 4) int efi_snprintf(efi_char16_t *buf, size_t size, const char *fmt, ...);
 
 void efi_free(unsigned long size, unsigned long addr);
 DEFINE_FREE(efi_pool, void *, if (_T) efi_bs_call(free_pool, _T));
diff --git a/drivers/firmware/efi/libstub/vsprintf.c b/drivers/firmware/efi/libstub/vsprintf.c
index 54b82ba798a2..071c8b245b68 100644
--- a/drivers/firmware/efi/libstub/vsprintf.c
+++ b/drivers/firmware/efi/libstub/vsprintf.c
@@ -508,3 +508,14 @@ int efi_vsnprintf(efi_char16_t *buf, size_t size, const char *fmt, va_list ap,
 
 	return pos;
 }
+
+int efi_snprintf(efi_char16_t *buf, size_t size, const char *fmt, ...)
+{
+       va_list args;
+       int i;
+
+       va_start(args, fmt);
+       i = efi_vsnprintf(buf, size, fmt, args, false);
+       va_end(args);
+       return i;
+}
-- 
2.55.0.1032.g73a4cd73de-goog