macro: introduce TAKE_PTR() macro

This macro will read a pointer of any type, return it, and set the
pointer to NULL. This is useful as an explicit concept of passing
ownership of a memory area between pointers.

This takes inspiration from Rust:

https://doc.rust-lang.org/std/option/enum.Option.html#method.take

and was suggested by Alan Jenkins (@sourcejedi).

It drops ~160 lines of code from our codebase, which makes me like it.
Also, I think it clarifies passing of ownership, and thus helps
readability a bit (at least for the initiated who know the new macro)

1 files changed, 2 insertions, 4 deletions

diff --git a/src/shared/efivars.c b/src/shared/efivars.c
index 9ca51cf750..d31cf2d860 100644
--- a/src/shared/efivars.c
+++ b/src/shared/efivars.c
@@ -249,8 +249,7 @@ int efi_get_variable(
         ((char*) buf)[st.st_size - 4] = 0;
         ((char*) buf)[st.st_size - 4 + 1] = 0;
 
-        *value = buf;
-        buf = NULL;
+        *value = TAKE_PTR(buf);
         *size = (size_t) st.st_size - 4;
 
         if (attribute)
@@ -563,8 +562,7 @@ int efi_get_boot_order(uint16_t **order) {
             l / sizeof(uint16_t) > INT_MAX)
                 return -EINVAL;
 
-        *order = buf;
-        buf = NULL;
+        *order = TAKE_PTR(buf);
         return (int) (l / sizeof(uint16_t));
 }