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steam-launch-wrapper starts every game with --oom-score-adjust 900; on Android 900 is CACHED_APP_MIN_ADJ, so lmkd kills the running game first when memory runs short (and on Linux 6.1 the raise becomes the process's permanent minimum). A process in the app cannot go below the score it inherits, so the writes that succeed from inside are raises: every write-open of /proc/<pid|self|thread-self>[/task/<tid>]/oom_score_adj (or oom_adj), through open/openat or fopen, goes to /dev/null, logged once. Based on the oom_score_adj redirect in the preload's opens.c by jdmg28 (https://github.com/jdmg28/DroidDeck-Mali/commit/6be00e00)
48 lines
1.7 KiB
C
48 lines
1.7 KiB
C
/*
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* Based on jdmg28's DroidDeck-Mali fork (commit 6be00e00, GPL-3.0): steam-launch-wrapper runs every
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* game with --oom-score-adjust 900. Android's lmkd reads 900 as CACHED_APP_MIN_ADJ and kills the
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* foreground game first when memory runs short; on Linux 6.1 the raise also becomes the process's
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* permanent minimum. An app's processes cannot go below the score they inherit, so the only writes
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* that succeed from in here are raises: every write-open of an oom_score_adj file goes to /dev/null.
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*/
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#define _GNU_SOURCE
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#include <errno.h>
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#include <string.h>
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#include <unistd.h>
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static int is_oom_score_adj(const char *path) {
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if (path == NULL || strncmp(path, "/proc/", 6) != 0) return 0;
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const char *p = path + 6;
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if (strncmp(p, "self/", 5) == 0) {
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p += 5;
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} else if (strncmp(p, "thread-self/", 12) == 0) {
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p += 12;
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} else {
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const char *digits = p;
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while (*p >= '0' && *p <= '9') p++;
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if (p == digits || *p != '/') return 0;
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p++;
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if (strncmp(p, "task/", 5) == 0) {
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p += 5;
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digits = p;
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while (*p >= '0' && *p <= '9') p++;
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if (p == digits || *p != '/') return 0;
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p++;
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}
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}
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return strcmp(p, "oom_score_adj") == 0 || strcmp(p, "oom_adj") == 0;
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}
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__attribute__((visibility("hidden"))) const char *bl_oom_adj_redirect(const char *path, int writing) {
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static int logged;
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if (!writing || !is_oom_score_adj(path)) return path;
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if (!__atomic_exchange_n(&logged, 1, __ATOMIC_RELAXED)) {
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static const char msg[] = "droiddeck: an oom_score_adj raise was dropped (Android would treat this program as a cached app)\n";
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int saved = errno;
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ssize_t ignored = write(STDERR_FILENO, msg, sizeof(msg) - 1);
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(void)ignored;
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errno = saved;
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}
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return "/dev/null";
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}
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