sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 495 insertions, 0 deletions

diff --git a/scripts/dtc/util.c b/scripts/dtc/util.c
new file mode 100644
index 000000000..412592320
--- /dev/null
+++ b/scripts/dtc/util.c
@@ -0,0 +1,495 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2011 The Chromium Authors, All Rights Reserved.
+ * Copyright 2008 Jon Loeliger, Freescale Semiconductor, Inc.
+ *
+ * util_is_printable_string contributed by
+ *	Pantelis Antoniou <pantelis.antoniou AT gmail.com>
+ */
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <assert.h>
+#include <inttypes.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "libfdt.h"
+#include "util.h"
+#include "version_gen.h"
+
+void fprint_path_escaped(FILE *fp, const char *path)
+{
+	const char *p = path;
+
+	while (*p) {
+		if (*p == ' ') {
+			fputc('\\', fp);
+			fputc(' ', fp);
+		} else {
+			fputc(*p, fp);
+		}
+
+		p++;
+	}
+}
+
+char *xstrdup(const char *s)
+{
+	int len = strlen(s) + 1;
+	char *d = xmalloc(len);
+
+	memcpy(d, s, len);
+
+	return d;
+}
+
+char *xstrndup(const char *s, size_t n)
+{
+	size_t len = strnlen(s, n) + 1;
+	char *d = xmalloc(len);
+
+	memcpy(d, s, len - 1);
+	d[len - 1] = '\0';
+
+	return d;
+}
+
+int xavsprintf_append(char **strp, const char *fmt, va_list ap)
+{
+	int n, size = 0;	/* start with 128 bytes */
+	char *p;
+	va_list ap_copy;
+
+	p = *strp;
+	if (p)
+		size = strlen(p);
+
+	va_copy(ap_copy, ap);
+	n = vsnprintf(NULL, 0, fmt, ap_copy) + 1;
+	va_end(ap_copy);
+
+	p = xrealloc(p, size + n);
+
+	n = vsnprintf(p + size, n, fmt, ap);
+
+	*strp = p;
+	return strlen(p);
+}
+
+int xasprintf_append(char **strp, const char *fmt, ...)
+{
+	int n;
+	va_list ap;
+
+	va_start(ap, fmt);
+	n = xavsprintf_append(strp, fmt, ap);
+	va_end(ap);
+
+	return n;
+}
+
+int xasprintf(char **strp, const char *fmt, ...)
+{
+	int n;
+	va_list ap;
+
+	*strp = NULL;
+
+	va_start(ap, fmt);
+	n = xavsprintf_append(strp, fmt, ap);
+	va_end(ap);
+
+	return n;
+}
+
+char *join_path(const char *path, const char *name)
+{
+	int lenp = strlen(path);
+	int lenn = strlen(name);
+	int len;
+	int needslash = 1;
+	char *str;
+
+	len = lenp + lenn + 2;
+	if ((lenp > 0) && (path[lenp-1] == '/')) {
+		needslash = 0;
+		len--;
+	}
+
+	str = xmalloc(len);
+	memcpy(str, path, lenp);
+	if (needslash) {
+		str[lenp] = '/';
+		lenp++;
+	}
+	memcpy(str+lenp, name, lenn+1);
+	return str;
+}
+
+bool util_is_printable_string(const void *data, int len)
+{
+	const char *s = data;
+	const char *ss, *se;
+
+	/* zero length is not */
+	if (len == 0)
+		return 0;
+
+	/* must terminate with zero */
+	if (s[len - 1] != '\0')
+		return 0;
+
+	se = s + len;
+
+	while (s < se) {
+		ss = s;
+		while (s < se && *s && isprint((unsigned char)*s))
+			s++;
+
+		/* not zero, or not done yet */
+		if (*s != '\0' || s == ss)
+			return 0;
+
+		s++;
+	}
+
+	return 1;
+}
+
+/*
+ * Parse a octal encoded character starting at index i in string s.  The
+ * resulting character will be returned and the index i will be updated to
+ * point at the character directly after the end of the encoding, this may be
+ * the '\0' terminator of the string.
+ */
+static char get_oct_char(const char *s, int *i)
+{
+	char x[4];
+	char *endx;
+	long val;
+
+	x[3] = '\0';
+	strncpy(x, s + *i, 3);
+
+	val = strtol(x, &endx, 8);
+
+	assert(endx > x);
+
+	(*i) += endx - x;
+	return val;
+}
+
+/*
+ * Parse a hexadecimal encoded character starting at index i in string s.  The
+ * resulting character will be returned and the index i will be updated to
+ * point at the character directly after the end of the encoding, this may be
+ * the '\0' terminator of the string.
+ */
+static char get_hex_char(const char *s, int *i)
+{
+	char x[3];
+	char *endx;
+	long val;
+
+	x[2] = '\0';
+	strncpy(x, s + *i, 2);
+
+	val = strtol(x, &endx, 16);
+	if (!(endx  > x))
+		die("\\x used with no following hex digits\n");
+
+	(*i) += endx - x;
+	return val;
+}
+
+char get_escape_char(const char *s, int *i)
+{
+	char	c = s[*i];
+	int	j = *i + 1;
+	char	val;
+
+	switch (c) {
+	case 'a':
+		val = '\a';
+		break;
+	case 'b':
+		val = '\b';
+		break;
+	case 't':
+		val = '\t';
+		break;
+	case 'n':
+		val = '\n';
+		break;
+	case 'v':
+		val = '\v';
+		break;
+	case 'f':
+		val = '\f';
+		break;
+	case 'r':
+		val = '\r';
+		break;
+	case '0':
+	case '1':
+	case '2':
+	case '3':
+	case '4':
+	case '5':
+	case '6':
+	case '7':
+		j--; /* need to re-read the first digit as
+		      * part of the octal value */
+		val = get_oct_char(s, &j);
+		break;
+	case 'x':
+		val = get_hex_char(s, &j);
+		break;
+	default:
+		val = c;
+	}
+
+	(*i) = j;
+	return val;
+}
+
+int utilfdt_read_err(const char *filename, char **buffp, size_t *len)
+{
+	int fd = 0;	/* assume stdin */
+	char *buf = NULL;
+	size_t bufsize = 1024, offset = 0;
+	int ret = 0;
+
+	*buffp = NULL;
+	if (strcmp(filename, "-") != 0) {
+		fd = open(filename, O_RDONLY);
+		if (fd < 0)
+			return errno;
+	}
+
+	/* Loop until we have read everything */
+	buf = xmalloc(bufsize);
+	do {
+		/* Expand the buffer to hold the next chunk */
+		if (offset == bufsize) {
+			bufsize *= 2;
+			buf = xrealloc(buf, bufsize);
+		}
+
+		ret = read(fd, &buf[offset], bufsize - offset);
+		if (ret < 0) {
+			ret = errno;
+			break;
+		}
+		offset += ret;
+	} while (ret != 0);
+
+	/* Clean up, including closing stdin; return errno on error */
+	close(fd);
+	if (ret)
+		free(buf);
+	else
+		*buffp = buf;
+	if (len)
+		*len = bufsize;
+	return ret;
+}
+
+char *utilfdt_read(const char *filename, size_t *len)
+{
+	char *buff;
+	int ret = utilfdt_read_err(filename, &buff, len);
+
+	if (ret) {
+		fprintf(stderr, "Couldn't open blob from '%s': %s\n", filename,
+			strerror(ret));
+		return NULL;
+	}
+	/* Successful read */
+	return buff;
+}
+
+int utilfdt_write_err(const char *filename, const void *blob)
+{
+	int fd = 1;	/* assume stdout */
+	int totalsize;
+	int offset;
+	int ret = 0;
+	const char *ptr = blob;
+
+	if (strcmp(filename, "-") != 0) {
+		fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
+		if (fd < 0)
+			return errno;
+	}
+
+	totalsize = fdt_totalsize(blob);
+	offset = 0;
+
+	while (offset < totalsize) {
+		ret = write(fd, ptr + offset, totalsize - offset);
+		if (ret < 0) {
+			ret = -errno;
+			break;
+		}
+		offset += ret;
+	}
+	/* Close the file/stdin; return errno on error */
+	if (fd != 1)
+		close(fd);
+	return ret < 0 ? -ret : 0;
+}
+
+
+int utilfdt_write(const char *filename, const void *blob)
+{
+	int ret = utilfdt_write_err(filename, blob);
+
+	if (ret) {
+		fprintf(stderr, "Couldn't write blob to '%s': %s\n", filename,
+			strerror(ret));
+	}
+	return ret ? -1 : 0;
+}
+
+int utilfdt_decode_type(const char *fmt, int *type, int *size)
+{
+	int qualifier = 0;
+
+	if (!*fmt)
+		return -1;
+
+	/* get the conversion qualifier */
+	*size = -1;
+	if (strchr("hlLb", *fmt)) {
+		qualifier = *fmt++;
+		if (qualifier == *fmt) {
+			switch (*fmt++) {
+/* TODO:		case 'l': qualifier = 'L'; break;*/
+			case 'h':
+				qualifier = 'b';
+				break;
+			}
+		}
+	}
+
+	/* we should now have a type */
+	if ((*fmt == '\0') || !strchr("iuxsr", *fmt))
+		return -1;
+
+	/* convert qualifier (bhL) to byte size */
+	if (*fmt != 's' && *fmt != 'r')
+		*size = qualifier == 'b' ? 1 :
+				qualifier == 'h' ? 2 :
+				qualifier == 'l' ? 4 : -1;
+	*type = *fmt++;
+
+	/* that should be it! */
+	if (*fmt)
+		return -1;
+	return 0;
+}
+
+void utilfdt_print_data(const char *data, int len)
+{
+	int i;
+	const char *s;
+
+	/* no data, don't print */
+	if (len == 0)
+		return;
+
+	if (util_is_printable_string(data, len)) {
+		printf(" = ");
+
+		s = data;
+		do {
+			printf("\"%s\"", s);
+			s += strlen(s) + 1;
+			if (s < data + len)
+				printf(", ");
+		} while (s < data + len);
+
+	} else if ((len % 4) == 0) {
+		const fdt32_t *cell = (const fdt32_t *)data;
+
+		printf(" = <");
+		for (i = 0, len /= 4; i < len; i++)
+			printf("0x%08" PRIx32 "%s", fdt32_to_cpu(cell[i]),
+			       i < (len - 1) ? " " : "");
+		printf(">");
+	} else {
+		const unsigned char *p = (const unsigned char *)data;
+		printf(" = [");
+		for (i = 0; i < len; i++)
+			printf("%02x%s", *p++, i < len - 1 ? " " : "");
+		printf("]");
+	}
+}
+
+void NORETURN util_version(void)
+{
+	printf("Version: %s\n", DTC_VERSION);
+	exit(0);
+}
+
+void NORETURN util_usage(const char *errmsg, const char *synopsis,
+			 const char *short_opts,
+			 struct option const long_opts[],
+			 const char * const opts_help[])
+{
+	FILE *fp = errmsg ? stderr : stdout;
+	const char a_arg[] = "<arg>";
+	size_t a_arg_len = strlen(a_arg) + 1;
+	size_t i;
+	int optlen;
+
+	fprintf(fp,
+		"Usage: %s\n"
+		"\n"
+		"Options: -[%s]\n", synopsis, short_opts);
+
+	/* prescan the --long opt length to auto-align */
+	optlen = 0;
+	for (i = 0; long_opts[i].name; ++i) {
+		/* +1 is for space between --opt and help text */
+		int l = strlen(long_opts[i].name) + 1;
+		if (long_opts[i].has_arg == a_argument)
+			l += a_arg_len;
+		if (optlen < l)
+			optlen = l;
+	}
+
+	for (i = 0; long_opts[i].name; ++i) {
+		/* helps when adding new applets or options */
+		assert(opts_help[i] != NULL);
+
+		/* first output the short flag if it has one */
+		if (long_opts[i].val > '~')
+			fprintf(fp, "      ");
+		else
+			fprintf(fp, "  -%c, ", long_opts[i].val);
+
+		/* then the long flag */
+		if (long_opts[i].has_arg == no_argument)
+			fprintf(fp, "--%-*s", optlen, long_opts[i].name);
+		else
+			fprintf(fp, "--%s %s%*s", long_opts[i].name, a_arg,
+				(int)(optlen - strlen(long_opts[i].name) - a_arg_len), "");
+
+		/* finally the help text */
+		fprintf(fp, "%s\n", opts_help[i]);
+	}
+
+	if (errmsg) {
+		fprintf(fp, "\nError: %s\n", errmsg);
+		exit(EXIT_FAILURE);
+	} else
+		exit(EXIT_SUCCESS);
+}