bionic: make property area expandable
The property area is initially one 4K region, automatically expanding as
needed up to 64 regions.
To avoid duplicating code, __system_property_area_init() now allocates
and initializes the first region (previously it was allocated in init's
init_property_area() and initialized in bionic). For testing purposes,
__system_property_set_filename() may be used to override the file used
to map in regions.
Signed-off-by: Greg Hackmann <ghackmann@google.com>
(cherry picked from commit d32969701be070c0161c2643ee3c3df16066bbb8)
Change-Id: I038d451fe8849b0c4863663eec6f57f6521bf4a7
diff --git a/libc/bionic/system_properties.c b/libc/bionic/system_properties.c
index 5197ef3..800c8b8 100644
--- a/libc/bionic/system_properties.c
+++ b/libc/bionic/system_properties.c
@@ -55,7 +55,6 @@
unsigned volatile serial;
unsigned magic;
unsigned version;
- unsigned reserved[4];
unsigned toc[1];
};
@@ -70,10 +69,9 @@
typedef struct prop_info prop_info;
static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
+static char property_filename[PATH_MAX] = PROP_FILENAME;
-static unsigned dummy_props = 0;
-
-prop_area *__system_property_area__ = (void*) &dummy_props;
+prop_area *__system_property_regions__[PA_REGION_COUNT] = { NULL, };
static int get_fd_from_env(void)
{
@@ -86,27 +84,79 @@
return atoi(env);
}
-void __system_property_area_init(void *data)
+static int map_prop_region_rw(size_t region)
{
- prop_area *pa = data;
+ prop_area *pa;
+ int fd;
+ size_t offset = region * PA_SIZE;
+
+ if (__system_property_regions__[region]) {
+ return 0;
+ }
+
+ /* dev is a tmpfs that we can use to carve a shared workspace
+ * out of, so let's do that...
+ */
+ fd = open(property_filename, O_RDWR | O_CREAT | O_NOFOLLOW, 0644);
+ if (fd < 0) {
+ if (errno == EACCES) {
+ /* for consistency with the case where the process has already
+ * mapped the page in and segfaults when trying to write to it
+ */
+ abort();
+ }
+ return -1;
+ }
+
+ if (ftruncate(fd, offset + PA_SIZE) < 0)
+ goto out;
+
+ pa = mmap(NULL, PA_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
+ if(pa == MAP_FAILED)
+ goto out;
+
memset(pa, 0, PA_SIZE);
pa->magic = PROP_AREA_MAGIC;
pa->version = PROP_AREA_VERSION;
/* plug into the lib property services */
- __system_property_area__ = pa;
+ __system_property_regions__[region] = pa;
+
+ close(fd);
+ return 0;
+
+out:
+ close(fd);
+ return -1;
}
-int __system_properties_init(void)
+int __system_property_set_filename(const char *filename)
+{
+ size_t len = strlen(filename);
+ if (len >= sizeof(property_filename))
+ return -1;
+
+ strcpy(property_filename, filename);
+ return 0;
+}
+
+int __system_property_area_init()
+{
+ return map_prop_region_rw(0);
+}
+
+static int map_prop_region(size_t region)
{
bool fromFile = true;
+ bool swapped;
+ size_t offset = region * PA_SIZE;
int result = -1;
- if(__system_property_area__ != ((void*) &dummy_props)) {
+ if(__system_property_regions__[region]) {
return 0;
}
- int fd = open(PROP_FILENAME, O_RDONLY | O_NOFOLLOW);
+ int fd = open(property_filename, O_RDONLY | O_NOFOLLOW);
if ((fd < 0) && (errno == ENOENT)) {
/*
@@ -133,23 +183,33 @@
if ((fd_stat.st_uid != 0)
|| (fd_stat.st_gid != 0)
- || ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0)) {
+ || ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0)
+ || (fd_stat.st_size < offset + PA_SIZE) ) {
goto cleanup;
}
- prop_area *pa = mmap(NULL, fd_stat.st_size, PROT_READ, MAP_SHARED, fd, 0);
+ prop_area *pa = mmap(NULL, PA_SIZE, PROT_READ, MAP_SHARED, fd, offset);
if (pa == MAP_FAILED) {
goto cleanup;
}
if((pa->magic != PROP_AREA_MAGIC) || (pa->version != PROP_AREA_VERSION)) {
- munmap(pa, fd_stat.st_size);
+ munmap(pa, PA_SIZE);
goto cleanup;
}
- __system_property_area__ = pa;
result = 0;
+ swapped = __sync_bool_compare_and_swap(&__system_property_regions__[region],
+ NULL, pa);
+ if (!swapped) {
+ /**
+ * In the event of a race either mapping is equally good, so
+ * the thread that lost can just throw its mapping away and proceed as
+ * normal.
+ */
+ munmap(pa, PA_SIZE);
+ }
cleanup:
if (fromFile) {
@@ -159,17 +219,31 @@
return result;
}
+int __system_properties_init()
+{
+ return map_prop_region(0);
+}
+
int __system_property_foreach(
void (*propfn)(const prop_info *pi, void *cookie),
void *cookie)
{
- prop_area *pa = __system_property_area__;
- unsigned i;
+ size_t region;
- for (i = 0; i < pa->count; i++) {
- unsigned entry = pa->toc[i];
- prop_info *pi = TOC_TO_INFO(pa, entry);
- propfn(pi, cookie);
+ for (region = 0; region < PA_REGION_COUNT; region++) {
+ prop_area *pa;
+ unsigned i;
+
+ int err = map_prop_region(region);
+ if (err < 0)
+ break;
+ pa = __system_property_regions__[region];
+
+ for (i = 0; i < pa->count; i++) {
+ unsigned entry = pa->toc[i];
+ prop_info *pi = TOC_TO_INFO(pa, entry);
+ propfn(pi, cookie);
+ }
}
return 0;
@@ -177,9 +251,15 @@
const prop_info *__system_property_find_nth(unsigned n)
{
- prop_area *pa = __system_property_area__;
+ size_t region = n / PA_COUNT_MAX;
+ prop_area *pa;
- if(n >= pa->count) {
+ int err = map_prop_region(region);
+ if (err < 0)
+ return NULL;
+ pa = __system_property_regions__[region];
+
+ if((n % PA_COUNT_MAX) >= pa->count) {
return 0;
} else {
return TOC_TO_INFO(pa, pa->toc[n]);
@@ -188,25 +268,36 @@
const prop_info *__system_property_find(const char *name)
{
- prop_area *pa = __system_property_area__;
- unsigned count = pa->count;
- unsigned *toc = pa->toc;
unsigned len = strlen(name);
- prop_info *pi;
+ size_t region;
if (len >= PROP_NAME_MAX)
return 0;
if (len < 1)
return 0;
- while(count--) {
- unsigned entry = *toc++;
- if(TOC_NAME_LEN(entry) != len) continue;
+ for (region = 0; region < PA_REGION_COUNT; region++) {
+ prop_area *pa;
+ unsigned count;
+ unsigned *toc;
+ prop_info *pi;
- pi = TOC_TO_INFO(pa, entry);
- if(memcmp(name, pi->name, len)) continue;
+ int err = map_prop_region(region);
+ if (err < 0)
+ return 0;
+ pa = __system_property_regions__[region];
+ count = pa->count;
+ toc = pa->toc;
- return pi;
+ while(count--) {
+ unsigned entry = *toc++;
+ if(TOC_NAME_LEN(entry) != len) continue;
+
+ pi = TOC_TO_INFO(pa, entry);
+ if(memcmp(name, pi->name, len)) continue;
+
+ return pi;
+ }
}
return 0;
@@ -333,7 +424,7 @@
{
unsigned n;
if(pi == 0) {
- prop_area *pa = __system_property_area__;
+ prop_area *pa = __system_property_regions__[0];
n = pa->serial;
do {
__futex_wait(&pa->serial, n, 0);
@@ -349,7 +440,7 @@
int __system_property_update(prop_info *pi, const char *value, unsigned int len)
{
- prop_area *pa = __system_property_area__;
+ prop_area *pa = __system_property_regions__[0];
if (len >= PROP_VALUE_MAX)
return -1;
@@ -368,12 +459,11 @@
int __system_property_add(const char *name, unsigned int namelen,
const char *value, unsigned int valuelen)
{
- prop_area *pa = __system_property_area__;
- prop_info *pa_info_array = (void*) (((char*) pa) + PA_INFO_START);
+ prop_area *pa;
+ prop_info *pa_info_array;
prop_info *pi;
+ size_t region;
- if (pa->count == PA_COUNT_MAX)
- return -1;
if (namelen >= PROP_NAME_MAX)
return -1;
if (valuelen >= PROP_VALUE_MAX)
@@ -381,13 +471,28 @@
if (namelen < 1)
return -1;
+ for (region = 0; region < PA_REGION_COUNT; region++)
+ {
+ int err = map_prop_region_rw(region);
+ if (err < 0)
+ return -1;
+
+ pa = __system_property_regions__[region];
+
+ if (pa->count < PA_COUNT_MAX)
+ break;
+ }
+
+ if (region == PA_REGION_COUNT)
+ return -1;
+
+ pa_info_array = (void*) (((char*) pa) + PA_INFO_START);
pi = pa_info_array + pa->count;
pi->serial = (valuelen << 24);
memcpy(pi->name, name, namelen + 1);
memcpy(pi->value, value, valuelen + 1);
- pa->toc[pa->count] =
- (namelen << 24) | (((unsigned) pi) - ((unsigned) pa));
+ pa->toc[pa->count] = (namelen << 24) | (((unsigned) pi) - ((unsigned) pa));
pa->count++;
pa->serial++;
@@ -403,7 +508,7 @@
unsigned int __system_property_wait_any(unsigned int serial)
{
- prop_area *pa = __system_property_area__;
+ prop_area *pa = __system_property_regions__[0];
do {
__futex_wait(&pa->serial, serial, 0);