git/wrapper.c
Derrick Stolee 89024a0ab0 maintenance: add get_random_minute()
When we initially created background maintenance -- with its hourly,
daily, and weekly schedules -- we considered the effects of all clients
launching fetches to the server every hour on the hour. The worry of
DDoSing server hosts was noted, but left as something we would consider
for a future update.

As background maintenance has gained more adoption over the past three
years, our worries about DDoSing the big Git hosts has been unfounded.
Those systems, especially those serving public repositories, are already
resilient to thundering herds of much smaller scale.

However, sometimes organizations spin up specific custom server
infrastructure either in addition to or on top of their Git host. Some
of these technologies are built for a different range of scale, and can
hit concurrency limits sooner. Organizations with such custom
infrastructures are more likely to recommend tools like `scalar` which
furthers their adoption of background maintenance.

To help solve for this, create get_random_minute() as a method to help
Git select a random minute when creating schedules in the future. The
integrations with this method do not yet exist, but will follow in
future changes.

To avoid multiple sources of randomness in the Git codebase, create a
new helper function, git_rand(), that returns a random uint32_t. This is
similar to how rand() returns a random nonnegative value, except it is
based on csprng_bytes() which is cryptographic and will return values
larger than RAND_MAX.

One thing that is important for testability is that we notice when we
are under a test scenario and return a predictable result. The schedules
themselves are not checked for this value, but at least one launchctl
test checks that we do not unnecessarily reboot the schedule if it has
not changed from a previous version.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-08-10 14:04:16 -07:00

832 lines
17 KiB
C

/*
* Various trivial helper wrappers around standard functions
*/
#include "git-compat-util.h"
#include "abspath.h"
#include "config.h"
#include "gettext.h"
#include "object.h"
#include "repository.h"
#include "strbuf.h"
#include "trace2.h"
#ifdef HAVE_RTLGENRANDOM
/* This is required to get access to RtlGenRandom. */
#define SystemFunction036 NTAPI SystemFunction036
#include <ntsecapi.h>
#undef SystemFunction036
#endif
static int memory_limit_check(size_t size, int gentle)
{
static size_t limit = 0;
if (!limit) {
limit = git_env_ulong("GIT_ALLOC_LIMIT", 0);
if (!limit)
limit = SIZE_MAX;
}
if (size > limit) {
if (gentle) {
error("attempting to allocate %"PRIuMAX" over limit %"PRIuMAX,
(uintmax_t)size, (uintmax_t)limit);
return -1;
} else
die("attempting to allocate %"PRIuMAX" over limit %"PRIuMAX,
(uintmax_t)size, (uintmax_t)limit);
}
return 0;
}
char *xstrdup(const char *str)
{
char *ret = strdup(str);
if (!ret)
die("Out of memory, strdup failed");
return ret;
}
static void *do_xmalloc(size_t size, int gentle)
{
void *ret;
if (memory_limit_check(size, gentle))
return NULL;
ret = malloc(size);
if (!ret && !size)
ret = malloc(1);
if (!ret) {
if (!gentle)
die("Out of memory, malloc failed (tried to allocate %lu bytes)",
(unsigned long)size);
else {
error("Out of memory, malloc failed (tried to allocate %lu bytes)",
(unsigned long)size);
return NULL;
}
}
#ifdef XMALLOC_POISON
memset(ret, 0xA5, size);
#endif
return ret;
}
void *xmalloc(size_t size)
{
return do_xmalloc(size, 0);
}
static void *do_xmallocz(size_t size, int gentle)
{
void *ret;
if (unsigned_add_overflows(size, 1)) {
if (gentle) {
error("Data too large to fit into virtual memory space.");
return NULL;
} else
die("Data too large to fit into virtual memory space.");
}
ret = do_xmalloc(size + 1, gentle);
if (ret)
((char*)ret)[size] = 0;
return ret;
}
void *xmallocz(size_t size)
{
return do_xmallocz(size, 0);
}
void *xmallocz_gently(size_t size)
{
return do_xmallocz(size, 1);
}
/*
* xmemdupz() allocates (len + 1) bytes of memory, duplicates "len" bytes of
* "data" to the allocated memory, zero terminates the allocated memory,
* and returns a pointer to the allocated memory. If the allocation fails,
* the program dies.
*/
void *xmemdupz(const void *data, size_t len)
{
return memcpy(xmallocz(len), data, len);
}
char *xstrndup(const char *str, size_t len)
{
char *p = memchr(str, '\0', len);
return xmemdupz(str, p ? p - str : len);
}
int xstrncmpz(const char *s, const char *t, size_t len)
{
int res = strncmp(s, t, len);
if (res)
return res;
return s[len] == '\0' ? 0 : 1;
}
void *xrealloc(void *ptr, size_t size)
{
void *ret;
if (!size) {
free(ptr);
return xmalloc(0);
}
memory_limit_check(size, 0);
ret = realloc(ptr, size);
if (!ret)
die("Out of memory, realloc failed");
return ret;
}
void *xcalloc(size_t nmemb, size_t size)
{
void *ret;
if (unsigned_mult_overflows(nmemb, size))
die("data too large to fit into virtual memory space");
memory_limit_check(size * nmemb, 0);
ret = calloc(nmemb, size);
if (!ret && (!nmemb || !size))
ret = calloc(1, 1);
if (!ret)
die("Out of memory, calloc failed");
return ret;
}
void xsetenv(const char *name, const char *value, int overwrite)
{
if (setenv(name, value, overwrite))
die_errno(_("could not setenv '%s'"), name ? name : "(null)");
}
/**
* xopen() is the same as open(), but it die()s if the open() fails.
*/
int xopen(const char *path, int oflag, ...)
{
mode_t mode = 0;
va_list ap;
/*
* va_arg() will have undefined behavior if the specified type is not
* compatible with the argument type. Since integers are promoted to
* ints, we fetch the next argument as an int, and then cast it to a
* mode_t to avoid undefined behavior.
*/
va_start(ap, oflag);
if (oflag & O_CREAT)
mode = va_arg(ap, int);
va_end(ap);
for (;;) {
int fd = open(path, oflag, mode);
if (fd >= 0)
return fd;
if (errno == EINTR)
continue;
if ((oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))
die_errno(_("unable to create '%s'"), path);
else if ((oflag & O_RDWR) == O_RDWR)
die_errno(_("could not open '%s' for reading and writing"), path);
else if ((oflag & O_WRONLY) == O_WRONLY)
die_errno(_("could not open '%s' for writing"), path);
else
die_errno(_("could not open '%s' for reading"), path);
}
}
static int handle_nonblock(int fd, short poll_events, int err)
{
struct pollfd pfd;
if (err != EAGAIN && err != EWOULDBLOCK)
return 0;
pfd.fd = fd;
pfd.events = poll_events;
/*
* no need to check for errors, here;
* a subsequent read/write will detect unrecoverable errors
*/
poll(&pfd, 1, -1);
return 1;
}
/*
* xread() is the same a read(), but it automatically restarts read()
* operations with a recoverable error (EAGAIN and EINTR). xread()
* DOES NOT GUARANTEE that "len" bytes is read even if the data is available.
*/
ssize_t xread(int fd, void *buf, size_t len)
{
ssize_t nr;
if (len > MAX_IO_SIZE)
len = MAX_IO_SIZE;
while (1) {
nr = read(fd, buf, len);
if (nr < 0) {
if (errno == EINTR)
continue;
if (handle_nonblock(fd, POLLIN, errno))
continue;
}
return nr;
}
}
/*
* xwrite() is the same a write(), but it automatically restarts write()
* operations with a recoverable error (EAGAIN and EINTR). xwrite() DOES NOT
* GUARANTEE that "len" bytes is written even if the operation is successful.
*/
ssize_t xwrite(int fd, const void *buf, size_t len)
{
ssize_t nr;
if (len > MAX_IO_SIZE)
len = MAX_IO_SIZE;
while (1) {
nr = write(fd, buf, len);
if (nr < 0) {
if (errno == EINTR)
continue;
if (handle_nonblock(fd, POLLOUT, errno))
continue;
}
return nr;
}
}
/*
* xpread() is the same as pread(), but it automatically restarts pread()
* operations with a recoverable error (EAGAIN and EINTR). xpread() DOES
* NOT GUARANTEE that "len" bytes is read even if the data is available.
*/
ssize_t xpread(int fd, void *buf, size_t len, off_t offset)
{
ssize_t nr;
if (len > MAX_IO_SIZE)
len = MAX_IO_SIZE;
while (1) {
nr = pread(fd, buf, len, offset);
if ((nr < 0) && (errno == EAGAIN || errno == EINTR))
continue;
return nr;
}
}
ssize_t read_in_full(int fd, void *buf, size_t count)
{
char *p = buf;
ssize_t total = 0;
while (count > 0) {
ssize_t loaded = xread(fd, p, count);
if (loaded < 0)
return -1;
if (loaded == 0)
return total;
count -= loaded;
p += loaded;
total += loaded;
}
return total;
}
ssize_t write_in_full(int fd, const void *buf, size_t count)
{
const char *p = buf;
ssize_t total = 0;
while (count > 0) {
ssize_t written = xwrite(fd, p, count);
if (written < 0)
return -1;
if (!written) {
errno = ENOSPC;
return -1;
}
count -= written;
p += written;
total += written;
}
return total;
}
ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset)
{
char *p = buf;
ssize_t total = 0;
while (count > 0) {
ssize_t loaded = xpread(fd, p, count, offset);
if (loaded < 0)
return -1;
if (loaded == 0)
return total;
count -= loaded;
p += loaded;
total += loaded;
offset += loaded;
}
return total;
}
int xdup(int fd)
{
int ret = dup(fd);
if (ret < 0)
die_errno("dup failed");
return ret;
}
/**
* xfopen() is the same as fopen(), but it die()s if the fopen() fails.
*/
FILE *xfopen(const char *path, const char *mode)
{
for (;;) {
FILE *fp = fopen(path, mode);
if (fp)
return fp;
if (errno == EINTR)
continue;
if (*mode && mode[1] == '+')
die_errno(_("could not open '%s' for reading and writing"), path);
else if (*mode == 'w' || *mode == 'a')
die_errno(_("could not open '%s' for writing"), path);
else
die_errno(_("could not open '%s' for reading"), path);
}
}
FILE *xfdopen(int fd, const char *mode)
{
FILE *stream = fdopen(fd, mode);
if (!stream)
die_errno("Out of memory? fdopen failed");
return stream;
}
FILE *fopen_for_writing(const char *path)
{
FILE *ret = fopen(path, "w");
if (!ret && errno == EPERM) {
if (!unlink(path))
ret = fopen(path, "w");
else
errno = EPERM;
}
return ret;
}
static void warn_on_inaccessible(const char *path)
{
warning_errno(_("unable to access '%s'"), path);
}
int warn_on_fopen_errors(const char *path)
{
if (errno != ENOENT && errno != ENOTDIR) {
warn_on_inaccessible(path);
return -1;
}
return 0;
}
FILE *fopen_or_warn(const char *path, const char *mode)
{
FILE *fp = fopen(path, mode);
if (fp)
return fp;
warn_on_fopen_errors(path);
return NULL;
}
int xmkstemp(char *filename_template)
{
int fd;
char origtemplate[PATH_MAX];
strlcpy(origtemplate, filename_template, sizeof(origtemplate));
fd = mkstemp(filename_template);
if (fd < 0) {
int saved_errno = errno;
const char *nonrelative_template;
if (strlen(filename_template) != strlen(origtemplate))
filename_template = origtemplate;
nonrelative_template = absolute_path(filename_template);
errno = saved_errno;
die_errno("Unable to create temporary file '%s'",
nonrelative_template);
}
return fd;
}
/* Adapted from libiberty's mkstemp.c. */
#undef TMP_MAX
#define TMP_MAX 16384
int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
{
static const char letters[] =
"abcdefghijklmnopqrstuvwxyz"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"0123456789";
static const int num_letters = ARRAY_SIZE(letters) - 1;
static const char x_pattern[] = "XXXXXX";
static const int num_x = ARRAY_SIZE(x_pattern) - 1;
char *filename_template;
size_t len;
int fd, count;
len = strlen(pattern);
if (len < num_x + suffix_len) {
errno = EINVAL;
return -1;
}
if (strncmp(&pattern[len - num_x - suffix_len], x_pattern, num_x)) {
errno = EINVAL;
return -1;
}
/*
* Replace pattern's XXXXXX characters with randomness.
* Try TMP_MAX different filenames.
*/
filename_template = &pattern[len - num_x - suffix_len];
for (count = 0; count < TMP_MAX; ++count) {
int i;
uint64_t v;
if (csprng_bytes(&v, sizeof(v)) < 0)
return error_errno("unable to get random bytes for temporary file");
/* Fill in the random bits. */
for (i = 0; i < num_x; i++) {
filename_template[i] = letters[v % num_letters];
v /= num_letters;
}
fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
if (fd >= 0)
return fd;
/*
* Fatal error (EPERM, ENOSPC etc).
* It doesn't make sense to loop.
*/
if (errno != EEXIST)
break;
}
/* We return the null string if we can't find a unique file name. */
pattern[0] = '\0';
return -1;
}
int git_mkstemp_mode(char *pattern, int mode)
{
/* mkstemp is just mkstemps with no suffix */
return git_mkstemps_mode(pattern, 0, mode);
}
int xmkstemp_mode(char *filename_template, int mode)
{
int fd;
char origtemplate[PATH_MAX];
strlcpy(origtemplate, filename_template, sizeof(origtemplate));
fd = git_mkstemp_mode(filename_template, mode);
if (fd < 0) {
int saved_errno = errno;
const char *nonrelative_template;
if (!filename_template[0])
filename_template = origtemplate;
nonrelative_template = absolute_path(filename_template);
errno = saved_errno;
die_errno("Unable to create temporary file '%s'",
nonrelative_template);
}
return fd;
}
/*
* Some platforms return EINTR from fsync. Since fsync is invoked in some
* cases by a wrapper that dies on failure, do not expose EINTR to callers.
*/
static int fsync_loop(int fd)
{
int err;
do {
err = fsync(fd);
} while (err < 0 && errno == EINTR);
return err;
}
int git_fsync(int fd, enum fsync_action action)
{
switch (action) {
case FSYNC_WRITEOUT_ONLY:
trace2_counter_add(TRACE2_COUNTER_ID_FSYNC_WRITEOUT_ONLY, 1);
#ifdef __APPLE__
/*
* On macOS, fsync just causes filesystem cache writeback but
* does not flush hardware caches.
*/
return fsync_loop(fd);
#endif
#ifdef HAVE_SYNC_FILE_RANGE
/*
* On linux 2.6.17 and above, sync_file_range is the way to
* issue a writeback without a hardware flush. An offset of
* 0 and size of 0 indicates writeout of the entire file and the
* wait flags ensure that all dirty data is written to the disk
* (potentially in a disk-side cache) before we continue.
*/
return sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WAIT_BEFORE |
SYNC_FILE_RANGE_WRITE |
SYNC_FILE_RANGE_WAIT_AFTER);
#endif
#ifdef fsync_no_flush
return fsync_no_flush(fd);
#endif
errno = ENOSYS;
return -1;
case FSYNC_HARDWARE_FLUSH:
trace2_counter_add(TRACE2_COUNTER_ID_FSYNC_HARDWARE_FLUSH, 1);
/*
* On macOS, a special fcntl is required to really flush the
* caches within the storage controller. As of this writing,
* this is a very expensive operation on Apple SSDs.
*/
#ifdef __APPLE__
return fcntl(fd, F_FULLFSYNC);
#else
return fsync_loop(fd);
#endif
default:
BUG("unexpected git_fsync(%d) call", action);
}
}
static int warn_if_unremovable(const char *op, const char *file, int rc)
{
int err;
if (!rc || errno == ENOENT)
return 0;
err = errno;
warning_errno("unable to %s '%s'", op, file);
errno = err;
return rc;
}
int unlink_or_msg(const char *file, struct strbuf *err)
{
int rc = unlink(file);
assert(err);
if (!rc || errno == ENOENT)
return 0;
strbuf_addf(err, "unable to unlink '%s': %s",
file, strerror(errno));
return -1;
}
int unlink_or_warn(const char *file)
{
return warn_if_unremovable("unlink", file, unlink(file));
}
int rmdir_or_warn(const char *file)
{
return warn_if_unremovable("rmdir", file, rmdir(file));
}
int remove_or_warn(unsigned int mode, const char *file)
{
return S_ISGITLINK(mode) ? rmdir_or_warn(file) : unlink_or_warn(file);
}
static int access_error_is_ok(int err, unsigned flag)
{
return (is_missing_file_error(err) ||
((flag & ACCESS_EACCES_OK) && err == EACCES));
}
int access_or_warn(const char *path, int mode, unsigned flag)
{
int ret = access(path, mode);
if (ret && !access_error_is_ok(errno, flag))
warn_on_inaccessible(path);
return ret;
}
int access_or_die(const char *path, int mode, unsigned flag)
{
int ret = access(path, mode);
if (ret && !access_error_is_ok(errno, flag))
die_errno(_("unable to access '%s'"), path);
return ret;
}
char *xgetcwd(void)
{
struct strbuf sb = STRBUF_INIT;
if (strbuf_getcwd(&sb))
die_errno(_("unable to get current working directory"));
return strbuf_detach(&sb, NULL);
}
int xsnprintf(char *dst, size_t max, const char *fmt, ...)
{
va_list ap;
int len;
va_start(ap, fmt);
len = vsnprintf(dst, max, fmt, ap);
va_end(ap);
if (len < 0)
BUG("your snprintf is broken");
if (len >= max)
BUG("attempt to snprintf into too-small buffer");
return len;
}
void write_file_buf(const char *path, const char *buf, size_t len)
{
int fd = xopen(path, O_WRONLY | O_CREAT | O_TRUNC, 0666);
if (write_in_full(fd, buf, len) < 0)
die_errno(_("could not write to '%s'"), path);
if (close(fd))
die_errno(_("could not close '%s'"), path);
}
void write_file(const char *path, const char *fmt, ...)
{
va_list params;
struct strbuf sb = STRBUF_INIT;
va_start(params, fmt);
strbuf_vaddf(&sb, fmt, params);
va_end(params);
strbuf_complete_line(&sb);
write_file_buf(path, sb.buf, sb.len);
strbuf_release(&sb);
}
void sleep_millisec(int millisec)
{
poll(NULL, 0, millisec);
}
int xgethostname(char *buf, size_t len)
{
/*
* If the full hostname doesn't fit in buf, POSIX does not
* specify whether the buffer will be null-terminated, so to
* be safe, do it ourselves.
*/
int ret = gethostname(buf, len);
if (!ret)
buf[len - 1] = 0;
return ret;
}
int is_empty_or_missing_file(const char *filename)
{
struct stat st;
if (stat(filename, &st) < 0) {
if (errno == ENOENT)
return 1;
die_errno(_("could not stat %s"), filename);
}
return !st.st_size;
}
int open_nofollow(const char *path, int flags)
{
#ifdef O_NOFOLLOW
return open(path, flags | O_NOFOLLOW);
#else
struct stat st;
if (lstat(path, &st) < 0)
return -1;
if (S_ISLNK(st.st_mode)) {
errno = ELOOP;
return -1;
}
return open(path, flags);
#endif
}
int csprng_bytes(void *buf, size_t len)
{
#if defined(HAVE_ARC4RANDOM) || defined(HAVE_ARC4RANDOM_LIBBSD)
/* This function never returns an error. */
arc4random_buf(buf, len);
return 0;
#elif defined(HAVE_GETRANDOM)
ssize_t res;
char *p = buf;
while (len) {
res = getrandom(p, len, 0);
if (res < 0)
return -1;
len -= res;
p += res;
}
return 0;
#elif defined(HAVE_GETENTROPY)
int res;
char *p = buf;
while (len) {
/* getentropy has a maximum size of 256 bytes. */
size_t chunk = len < 256 ? len : 256;
res = getentropy(p, chunk);
if (res < 0)
return -1;
len -= chunk;
p += chunk;
}
return 0;
#elif defined(HAVE_RTLGENRANDOM)
if (!RtlGenRandom(buf, len))
return -1;
return 0;
#elif defined(HAVE_OPENSSL_CSPRNG)
int res = RAND_bytes(buf, len);
if (res == 1)
return 0;
if (res == -1)
errno = ENOTSUP;
else
errno = EIO;
return -1;
#else
ssize_t res;
char *p = buf;
int fd, err;
fd = open("/dev/urandom", O_RDONLY);
if (fd < 0)
return -1;
while (len) {
res = xread(fd, p, len);
if (res < 0) {
err = errno;
close(fd);
errno = err;
return -1;
}
len -= res;
p += res;
}
close(fd);
return 0;
#endif
}
uint32_t git_rand(void)
{
uint32_t result;
if (csprng_bytes(&result, sizeof(result)) < 0)
die(_("unable to get random bytes"));
return result;
}