alloc-util: simplify GREEDY_REALLOC() logic by relying on malloc_usable_size()

We recently started making more use of malloc_usable_size() and rely on
it (see the string_erase() story). Given that we don't really support
sytems where malloc_usable_size() cannot be trusted beyond statistics
anyway, let's go fully in and rework GREEDY_REALLOC() on top of it:
instead of passing around and maintaining the currenly allocated size
everywhere, let's just derive it automatically from
malloc_usable_size().

I am mostly after this for the simplicity this brings. It also brings
minor efficiency improvements I guess, but things become so much nicer
to look at if we can avoid these allocation size variables everywhere.

Note that the malloc_usable_size() man page says relying on it wasn't
"good programming practice", but I think it does this for reasons that
don't apply here: the greedy realloc logic specifically doesn't rely on
the returned extra size, beyond the fact that it is equal or larger than
what was requested.

(This commit was supposed to be a quick patch btw, but apparently we use
the greedy realloc stuff quite a bit across the codebase, so this ends
up touching *a*lot* of code.)

2 files changed, 3 insertions, 4 deletions

diff --git a/src/libsystemd/sd-device/device-enumerator.c b/src/libsystemd/sd-device/device-enumerator.c
index a290dbcc9c..3ae80ab942 100644
--- a/src/libsystemd/sd-device/device-enumerator.c
+++ b/src/libsystemd/sd-device/device-enumerator.c
@@ -29,7 +29,7 @@ struct sd_device_enumerator {
 
         DeviceEnumerationType type;
         sd_device **devices;
-        size_t n_devices, n_allocated, current_device_index;
+        size_t n_devices, current_device_index;
         bool scan_uptodate;
 
         Set *match_subsystem;
@@ -279,7 +279,7 @@ int device_enumerator_add_device(sd_device_enumerator *enumerator, sd_device *de
         assert_return(enumerator, -EINVAL);
         assert_return(device, -EINVAL);
 
-        if (!GREEDY_REALLOC(enumerator->devices, enumerator->n_allocated, enumerator->n_devices + 1))
+        if (!GREEDY_REALLOC(enumerator->devices, enumerator->n_devices + 1))
                 return -ENOMEM;
 
         enumerator->devices[enumerator->n_devices++] = sd_device_ref(device);
diff --git a/src/libsystemd/sd-device/device-private.c b/src/libsystemd/sd-device/device-private.c
index e612dbe0a0..09ef87f84c 100644
--- a/src/libsystemd/sd-device/device-private.c
+++ b/src/libsystemd/sd-device/device-private.c
@@ -480,7 +480,6 @@ static int device_update_properties_bufs(sd_device *device) {
         const char *val, *prop;
         _cleanup_free_ char **buf_strv = NULL;
         _cleanup_free_ uint8_t *buf_nulstr = NULL;
-        size_t allocated_nulstr = 0;
         size_t nulstr_len = 0, num = 0, i = 0;
 
         assert(device);
@@ -493,7 +492,7 @@ static int device_update_properties_bufs(sd_device *device) {
 
                 len = strlen(prop) + 1 + strlen(val);
 
-                buf_nulstr = GREEDY_REALLOC0(buf_nulstr, allocated_nulstr, nulstr_len + len + 2);
+                buf_nulstr = GREEDY_REALLOC0(buf_nulstr, nulstr_len + len + 2);
                 if (!buf_nulstr)
                         return -ENOMEM;