git/tempfile.c
Jeff King 320fa579ec tempfile: update comment describing state transitions
Back when 1a9d15db25 (tempfile: a new module for handling temporary
files, 2015-08-10) added this comment, tempfile structs were held in
memory for the life of a process, and there were various guarantees
about which fields were valid in which states.

Since 422a21c6a0 (tempfile: remove deactivated list entries, 2017-09-05)
and 076aa2cbda (tempfile: auto-allocate tempfiles on heap, 2017-09-05),
the flow is quite different: objects come and go from the list, and
inactive ones are deallocated. And the previous commit removed the
"active" flag from the struct entirely.

Let's bring the comment up to date with the current code.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-08-30 14:16:51 -07:00

367 lines
9.2 KiB
C

/*
* State diagram and cleanup
* -------------------------
*
* If the program exits while a temporary file is active, we want to
* make sure that we remove it. This is done by remembering the active
* temporary files in a linked list, `tempfile_list`. An `atexit(3)`
* handler and a signal handler are registered, to clean up any active
* temporary files.
*
* Because the signal handler can run at any time, `tempfile_list` and
* the `tempfile` objects that comprise it must be kept in
* self-consistent states at all times.
*
* The possible states of a `tempfile` object are as follows:
*
* - Inactive/unallocated. The only way to get a tempfile is via a creation
* function like create_tempfile(). Once allocated, the tempfile is on the
* global tempfile_list and considered active.
*
* - Active, file open (after `create_tempfile()` or
* `reopen_tempfile()`). In this state:
*
* - the temporary file exists
* - `filename` holds the filename of the temporary file
* - `fd` holds a file descriptor open for writing to it
* - `fp` holds a pointer to an open `FILE` object if and only if
* `fdopen_tempfile()` has been called on the object
* - `owner` holds the PID of the process that created the file
*
* - Active, file closed (after `close_tempfile_gently()`). Same
* as the previous state, except that the temporary file is closed,
* `fd` is -1, and `fp` is `NULL`.
*
* - Inactive (after `delete_tempfile()`, `rename_tempfile()`, or a
* failed attempt to create a temporary file). The struct is removed from
* the global tempfile_list and deallocated.
*
* A temporary file is owned by the process that created it. The
* `tempfile` has an `owner` field that records the owner's PID. This
* field is used to prevent a forked process from deleting a temporary
* file created by its parent.
*/
#include "cache.h"
#include "tempfile.h"
#include "sigchain.h"
static VOLATILE_LIST_HEAD(tempfile_list);
static void remove_template_directory(struct tempfile *tempfile,
int in_signal_handler)
{
if (tempfile->directory) {
if (in_signal_handler)
rmdir(tempfile->directory);
else
rmdir_or_warn(tempfile->directory);
}
}
static void remove_tempfiles(int in_signal_handler)
{
pid_t me = getpid();
volatile struct volatile_list_head *pos;
list_for_each(pos, &tempfile_list) {
struct tempfile *p = list_entry(pos, struct tempfile, list);
if (!is_tempfile_active(p) || p->owner != me)
continue;
if (p->fd >= 0)
close(p->fd);
if (in_signal_handler)
unlink(p->filename.buf);
else
unlink_or_warn(p->filename.buf);
remove_template_directory(p, in_signal_handler);
}
}
static void remove_tempfiles_on_exit(void)
{
remove_tempfiles(0);
}
static void remove_tempfiles_on_signal(int signo)
{
remove_tempfiles(1);
sigchain_pop(signo);
raise(signo);
}
static struct tempfile *new_tempfile(void)
{
struct tempfile *tempfile = xmalloc(sizeof(*tempfile));
tempfile->fd = -1;
tempfile->fp = NULL;
tempfile->owner = 0;
INIT_LIST_HEAD(&tempfile->list);
strbuf_init(&tempfile->filename, 0);
tempfile->directory = NULL;
return tempfile;
}
static void activate_tempfile(struct tempfile *tempfile)
{
static int initialized;
if (!initialized) {
sigchain_push_common(remove_tempfiles_on_signal);
atexit(remove_tempfiles_on_exit);
initialized = 1;
}
volatile_list_add(&tempfile->list, &tempfile_list);
tempfile->owner = getpid();
}
static void deactivate_tempfile(struct tempfile *tempfile)
{
volatile_list_del(&tempfile->list);
strbuf_release(&tempfile->filename);
free(tempfile->directory);
free(tempfile);
}
/* Make sure errno contains a meaningful value on error */
struct tempfile *create_tempfile_mode(const char *path, int mode)
{
struct tempfile *tempfile = new_tempfile();
strbuf_add_absolute_path(&tempfile->filename, path);
tempfile->fd = open(tempfile->filename.buf,
O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, mode);
if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
/* Try again w/o O_CLOEXEC: the kernel might not support it */
tempfile->fd = open(tempfile->filename.buf,
O_RDWR | O_CREAT | O_EXCL, mode);
if (tempfile->fd < 0) {
deactivate_tempfile(tempfile);
return NULL;
}
activate_tempfile(tempfile);
if (adjust_shared_perm(tempfile->filename.buf)) {
int save_errno = errno;
error("cannot fix permission bits on %s", tempfile->filename.buf);
delete_tempfile(&tempfile);
errno = save_errno;
return NULL;
}
return tempfile;
}
struct tempfile *register_tempfile(const char *path)
{
struct tempfile *tempfile = new_tempfile();
strbuf_add_absolute_path(&tempfile->filename, path);
activate_tempfile(tempfile);
return tempfile;
}
struct tempfile *mks_tempfile_sm(const char *filename_template, int suffixlen, int mode)
{
struct tempfile *tempfile = new_tempfile();
strbuf_add_absolute_path(&tempfile->filename, filename_template);
tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
if (tempfile->fd < 0) {
deactivate_tempfile(tempfile);
return NULL;
}
activate_tempfile(tempfile);
return tempfile;
}
struct tempfile *mks_tempfile_tsm(const char *filename_template, int suffixlen, int mode)
{
struct tempfile *tempfile = new_tempfile();
const char *tmpdir;
tmpdir = getenv("TMPDIR");
if (!tmpdir)
tmpdir = "/tmp";
strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, filename_template);
tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
if (tempfile->fd < 0) {
deactivate_tempfile(tempfile);
return NULL;
}
activate_tempfile(tempfile);
return tempfile;
}
struct tempfile *mks_tempfile_dt(const char *directory_template,
const char *filename)
{
struct tempfile *tempfile;
const char *tmpdir;
struct strbuf sb = STRBUF_INIT;
int fd;
size_t directorylen;
if (!ends_with(directory_template, "XXXXXX")) {
errno = EINVAL;
return NULL;
}
tmpdir = getenv("TMPDIR");
if (!tmpdir)
tmpdir = "/tmp";
strbuf_addf(&sb, "%s/%s", tmpdir, directory_template);
directorylen = sb.len;
if (!mkdtemp(sb.buf)) {
int orig_errno = errno;
strbuf_release(&sb);
errno = orig_errno;
return NULL;
}
strbuf_addf(&sb, "/%s", filename);
fd = open(sb.buf, O_CREAT | O_EXCL | O_RDWR, 0600);
if (fd < 0) {
int orig_errno = errno;
strbuf_setlen(&sb, directorylen);
rmdir(sb.buf);
strbuf_release(&sb);
errno = orig_errno;
return NULL;
}
tempfile = new_tempfile();
strbuf_swap(&tempfile->filename, &sb);
tempfile->directory = xmemdupz(tempfile->filename.buf, directorylen);
tempfile->fd = fd;
activate_tempfile(tempfile);
return tempfile;
}
struct tempfile *xmks_tempfile_m(const char *filename_template, int mode)
{
struct tempfile *tempfile;
struct strbuf full_template = STRBUF_INIT;
strbuf_add_absolute_path(&full_template, filename_template);
tempfile = mks_tempfile_m(full_template.buf, mode);
if (!tempfile)
die_errno("Unable to create temporary file '%s'",
full_template.buf);
strbuf_release(&full_template);
return tempfile;
}
FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
{
if (!is_tempfile_active(tempfile))
BUG("fdopen_tempfile() called for inactive object");
if (tempfile->fp)
BUG("fdopen_tempfile() called for open object");
tempfile->fp = fdopen(tempfile->fd, mode);
return tempfile->fp;
}
const char *get_tempfile_path(struct tempfile *tempfile)
{
if (!is_tempfile_active(tempfile))
BUG("get_tempfile_path() called for inactive object");
return tempfile->filename.buf;
}
int get_tempfile_fd(struct tempfile *tempfile)
{
if (!is_tempfile_active(tempfile))
BUG("get_tempfile_fd() called for inactive object");
return tempfile->fd;
}
FILE *get_tempfile_fp(struct tempfile *tempfile)
{
if (!is_tempfile_active(tempfile))
BUG("get_tempfile_fp() called for inactive object");
return tempfile->fp;
}
int close_tempfile_gently(struct tempfile *tempfile)
{
int fd;
FILE *fp;
int err;
if (!is_tempfile_active(tempfile) || tempfile->fd < 0)
return 0;
fd = tempfile->fd;
fp = tempfile->fp;
tempfile->fd = -1;
if (fp) {
tempfile->fp = NULL;
if (ferror(fp)) {
err = -1;
if (!fclose(fp))
errno = EIO;
} else {
err = fclose(fp);
}
} else {
err = close(fd);
}
return err ? -1 : 0;
}
int reopen_tempfile(struct tempfile *tempfile)
{
if (!is_tempfile_active(tempfile))
BUG("reopen_tempfile called for an inactive object");
if (0 <= tempfile->fd)
BUG("reopen_tempfile called for an open object");
tempfile->fd = open(tempfile->filename.buf, O_WRONLY|O_TRUNC);
return tempfile->fd;
}
int rename_tempfile(struct tempfile **tempfile_p, const char *path)
{
struct tempfile *tempfile = *tempfile_p;
if (!is_tempfile_active(tempfile))
BUG("rename_tempfile called for inactive object");
if (close_tempfile_gently(tempfile)) {
delete_tempfile(tempfile_p);
return -1;
}
if (rename(tempfile->filename.buf, path)) {
int save_errno = errno;
delete_tempfile(tempfile_p);
errno = save_errno;
return -1;
}
deactivate_tempfile(tempfile);
*tempfile_p = NULL;
return 0;
}
void delete_tempfile(struct tempfile **tempfile_p)
{
struct tempfile *tempfile = *tempfile_p;
if (!is_tempfile_active(tempfile))
return;
close_tempfile_gently(tempfile);
unlink_or_warn(tempfile->filename.buf);
remove_template_directory(tempfile, 0);
deactivate_tempfile(tempfile);
*tempfile_p = NULL;
}