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authorHristo Venev <hristo@venev.name>2021-07-23 16:51:04 +0300
committerHristo Venev <hristo@venev.name>2021-08-08 18:30:49 +0300
commit8c89da4825322660a912b717ba83326151e0866e (patch)
tree7dcb3a6fc56da030aaf2d0087c6b4857d989a994
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-rw-r--r--LICENSE165
-rw-r--r--LICENSE.GPL3674
-rw-r--r--Makefile40
-rw-r--r--README.md93
-rw-r--r--config.h16
-rw-r--r--pgbak.c569
-rw-r--r--test.py187
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diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+ GNU LESSER GENERAL PUBLIC LICENSE
+ Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
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+ This version of the GNU Lesser General Public License incorporates
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diff --git a/LICENSE.GPL3 b/LICENSE.GPL3
new file mode 100644
index 0000000..f288702
--- /dev/null
+++ b/LICENSE.GPL3
@@ -0,0 +1,674 @@
+ GNU GENERAL PUBLIC LICENSE
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+ An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations. If propagation of a covered
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+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+ You may not impose any further restrictions on the exercise of the
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+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+ 11. Patents.
+
+ A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based. The
+work thus licensed is called the contributor's "contributor version".
+
+ A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version. For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
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+
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+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+ In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement). To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+ If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients. "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+ If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+ A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License. You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+ Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+ 12. No Surrender of Others' Freedom.
+
+ If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License. If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all. For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+ 13. Use with the GNU Affero General Public License.
+
+ Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work. The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+ 14. Revised Versions of this License.
+
+ The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time. Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+ Each version is given a distinguishing version number. If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation. If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+ If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+ Later license versions may give you additional or different
+permissions. However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+ 15. Disclaimer of Warranty.
+
+ THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+ 16. Limitation of Liability.
+
+ IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+ 17. Interpretation of Sections 15 and 16.
+
+ If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) <year> <name of author>
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+ <program> Copyright (C) <year> <name of author>
+ This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+ The GNU General Public License does not permit incorporating your program
+into proprietary programs. If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License. But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..638e08d
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,40 @@
+CFLAGS_dev:= \
+ -std=gnu17 -Wall -Wextra \
+ -Werror=conversion \
+ -Werror=sign-conversion \
+ -Werror=float-conversion \
+ -Werror=old-style-definition \
+ -Werror=strict-prototypes \
+ -Werror=missing-prototypes \
+ -Werror=implicit-function-declaration \
+ -Werror=missing-declarations \
+ -Werror=return-type \
+ -Werror=pointer-arith \
+ -Werror=vla \
+ -Werror=incompatible-pointer-types \
+ -Werror=int-conversion \
+ -Werror=int-conversion \
+ -Werror=format=2 \
+ -Werror=overflow \
+ -Werror=shift-count-overflow \
+ -Werror=init-self \
+ -Werror=shadow \
+ -Werror=redundant-decls \
+ -Werror=missing-field-initializers \
+ -Werror=write-strings \
+ -Werror=date-time \
+ -Werror=nested-externs \
+ -Werror=endif-labels \
+ -Werror=undef \
+ -Wmissing-include-dirs \
+ -Wfloat-equal \
+ -Winline \
+ -Wmissing-noreturn \
+ -Werror=implicit-fallthrough \
+ -Werror=shift-overflow
+
+CC?=gcc
+CFLAGS?=-O2 -flto -ggdb
+
+pgbak: pgbak.c
+ $(CC) $(CFLAGS_dev) $(CFLAGS) $< -o $@
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..3040ca0
--- /dev/null
+++ b/README.md
@@ -0,0 +1,93 @@
+# pgbak
+
+## Overview
+
+`pgbak` is a utility for PostgreSQL backups based on WAL archiving. Data is stored in a local directory provided through the `PGBAK` environment variable.
+
+Note that `pgbak` itself does not back up the data to any remote location. Instead the user must provide a script at `$PGBAK/scripts/backup` which is invoked when a backup needs to be performed. If no remote backups are desired, it can simply be a symlink to `/bin/true`.
+
+## Backup directory structure
+
+- `$PGBAK/TIMESTAMP/` — One or more directories containing base backups and WAL segments. The `TIMESTAMP` is when the base backup was taken.
+ - `$PGBAK/TIMESTAMP/base.tzst` — A compressed tarball containing a full database backup as created by `pg_basebackup`.
+ - `$PGBAK/TIMESTAMP/pg_wal/NNN.zst` — One or more compressed WAL segments following the full backup.
+- `$PGBAK/current` — Symlink to the latest backup directory.
+- `$PGBAK/scripts/` — Directory for user-provided scripts.
+ - `$PGBAK/scripts/backup` — script called after one or more WAL files were archived; required
+- `$PGBAK/pgbak.lock` — Lock/state file. Locking is done through `fcntl()`, so deleting this file should never be necessary.
+
+Currently `pgbak` never deletes old backup directories.
+
+## Usage
+
+The following subcommands are provided:
+
+- `pgbak wal PATH` — Archive the given WAL file and exit. A background sync process will be started if one isn't running.
+- `pgbak sync` — Run sync in the foreground if necessary.
+- `pgbak force-sync` — Run sync in the foreground. The `backup` script is always invoked.
+- `pgbak wait [TIMEOUT]` — If a sync is running, wait for it to finish. The `TIMEOUT` is in seconds and defaults to infinity. Exits with non-zero status on error or timeout.
+
+The sync process is responsible for maintaining the `$PGBAK` directory. In particular, it
+
+- creates a new full backup every now and again
+- calls `$PGBAK/scripts/backup`
+
+### Writing `$PGBAK/scripts/backup`
+
+When the `backup` script is started, the current directory is set to the subdirectory of `$PGBAK` that needs to be backed up. The script is given the following arguments:
+
+- the timestamp of the base backup
+- the current timestamp
+
+Existing files will never disappear/change, provided the base backup timestamp is the same. However, new compressed WAL files may appear at any time. If this happens while the `backup` script is running, it will be called again with a refreshed current timestamp.
+
+On failure, the `backup` script will be retried indefinitely. The timestamps will be the same if no new WAL files have appeared.
+
+### Restoring from a backup
+
+In order to restore from a backup, simply extract `base.tzst` to an empty `$PGDATA` directory and uncompress all WAL files into `$PGDATA/pg_wal`.
+
+Recovery can take quite a while if many WAL files need to be replayed. It may be beneficial to do it without `fsync` and instead `sync` later:
+
+```sh
+mkdir -m700 data
+tar -C data -xf backup/base.tzst
+zstd -d --output-dir-flat data/pg_wal backup/pg_wal/*
+postgres --single -FD data < /dev/null
+sync -f data
+```
+
+## Example configuration
+
+`postgresql.conf`:
+```ini
+archive_mode = on
+archive_command = 'pgbak wal %p'
+archive_timeout = 1h
+```
+
+`postgresql.service`:
+```ini
+[Unit]
+# Make sure DNS works while postgres/pgbak is running
+After=nss-lookup.target
+
+[Service]
+Environment=PGBAK=/media/backup/pgsql
+# Wait up to 2 minutes for pgbak sync to finish after postgres is stopped.
+ExecStopPost=pgbak wait 120
+```
+
+`$PGBAK/scripts/backup`:
+```sh
+#!/bin/sh
+exec rsync -r ./ "backup@host.example:pg-$1/"
+```
+
+To make your first backup, simply restart postgres and call `pg_switch_wal()`.
+
+## Misc
+
+`pgbak` uses [Zstandard](http://www.zstd.net/)'s command-line tool for compression. The compression options may be tweaked in `config.h`.
+
+Currently only Linux is supported because of `O_TMPFILE` and `F_OFD_SETLK`.
diff --git a/config.h b/config.h
new file mode 100644
index 0000000..0dcd86b
--- /dev/null
+++ b/config.h
@@ -0,0 +1,16 @@
+static const char *const BASE_OUT = "base.tzst";
+static const char *const BASE_BACKUP_ARGV[] = {
+ "pg_basebackup",
+ "-F", "t",
+ "-X", "none",
+ "-D", "-",
+ NULL,
+};
+static const char *const BASE_COMPRESS_ARGV[] = {
+ "zstd", "-12", "-T0", NULL,
+};
+
+static const char *const WAL_EXT = ".zst";
+static const char *const WAL_COMPRESS_ARGV[] = {
+ "zstd", "-19", "--single-thread", NULL,
+};
diff --git a/pgbak.c b/pgbak.c
new file mode 100644
index 0000000..439d643
--- /dev/null
+++ b/pgbak.c
@@ -0,0 +1,569 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+//
+// Copyright 2021 Hristo Venev
+
+#define _GNU_SOURCE
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "config.h"
+
+static int backup_dfd;
+static int lck_fd;
+
+
+static const char *const LOCK_KIND[] = {
+ // The `state` lock must be held while doing state-related updates, for
+ // example modifying the "archive needed" flag.
+ "state",
+
+ // The `backup` lock is held by the archiver process.
+ "backup",
+
+ // The `wait` lock is acquired by the archiver process after the `backup`
+ // lock. It is also acquired by processes that wait for the archiver to
+ // finish.
+ "wait",
+};
+
+static void lck_release(int pos) {
+ struct flock l = {
+ .l_type = F_UNLCK,
+ .l_whence = SEEK_SET,
+ .l_start = pos,
+ .l_len = 1,
+ };
+ while(true) {
+ if(fcntl(lck_fd, F_OFD_SETLKW, &l) >= 0) return;
+ if(errno == EINTR) continue;
+ fprintf(stderr, "Failed to release %s lock: %m\n", LOCK_KIND[pos]);
+ abort();
+ }
+}
+
+static void lck_wait(int pos) {
+ struct flock l = {
+ .l_type = F_WRLCK,
+ .l_whence = SEEK_SET,
+ .l_start = pos,
+ .l_len = 1,
+ };
+ while(true) {
+ if(fcntl(lck_fd, F_OFD_SETLKW, &l) >= 0) return;
+ if(errno == EINTR) continue;
+ fprintf(stderr, "Failed to acquire %s lock: %m\n", LOCK_KIND[pos]);
+ abort();
+ }
+}
+
+static bool lck_try(int pos) {
+ struct flock l = {
+ .l_type = F_WRLCK,
+ .l_whence = SEEK_SET,
+ .l_start = pos,
+ .l_len = 1,
+ };
+ while(true) {
+ if(fcntl(lck_fd, F_OFD_SETLK, &l) >= 0) return true;
+ if(errno == EINTR) continue;
+ if(errno == EAGAIN || errno == EACCES) return false;
+ fprintf(stderr, "Failed to acquire %s lock: %m\n", LOCK_KIND[pos]);
+ abort();
+ }
+}
+
+static int lck_read(int pos) {
+ unsigned char b;
+ ssize_t r = pread(lck_fd, &b, 1, pos);
+ if(r < 0) {
+ fprintf(stderr, "Failed to read lock file: %m\n");
+ abort();
+ }
+ if(r >= 1) return b;
+ return -1;
+}
+
+static void lck_write(int pos, unsigned char b) {
+ ssize_t r = pwrite(lck_fd, &b, 1, pos);
+ if(r < 0) {
+ fprintf(stderr, "Failed to read lock file: %m\n");
+ abort();
+ }
+ if(r == 0) {
+ fprintf(stderr, "Failed to write lock file: Empty write\n");
+ abort();
+ }
+}
+
+static pid_t cld_spawn(int in_fd, int out_fd, int chdir_fd, const char *const *argv) {
+ pid_t child = fork();
+ if(child < 0) {
+ fprintf(stderr, "fork(): %m\n");
+ abort();
+ }
+ if(child == 0) {
+ if(chdir_fd >= 0 && fchdir(chdir_fd) < 0) _exit(1);
+ if(in_fd >= 0 && dup2(in_fd, 0) < 0) _exit(1);
+ if(out_fd >= 0 && dup2(out_fd, 1) < 0) _exit(1);
+ execvpe(argv[0], (char*const*)argv, environ);
+ _exit(1);
+ }
+ return child;
+}
+
+static int cld_wait(pid_t child, const char *cld) {
+ int status;
+ if(waitpid(child, &status, 0) < 0) {
+ fprintf(stderr, "waitpid(): %m\n");
+ abort();
+ }
+
+ if(WIFEXITED(status)) {
+ int r = WEXITSTATUS(status);
+ if(r) {
+ fprintf(stderr, "Child process '%s' exited with status %d\n", cld, r);
+ }
+ return r;
+ } else if(WIFSIGNALED(status)) {
+ int r = WTERMSIG(status);
+ fprintf(stderr, "Child process '%s' killed by signal %d\n", cld, r);
+ return 128 + r;
+ } else {
+ fprintf(stderr, "waitpid(): Unknown status\n");
+ abort();
+ }
+}
+
+static int cld_pipe(int in_fd, int out_fd, const char *const *argv) {
+ pid_t child = cld_spawn(in_fd, out_fd, -1, argv);
+ if(in_fd >= 0) close(in_fd);
+
+ int r = cld_wait(child, argv[0]);
+ if(r == 0 && out_fd >= 0 && fsync(out_fd) < 0) {
+ fprintf(stderr, "fsync(): %m\n");
+ r = -1;
+ }
+ return r;
+}
+
+
+static int bak_snapshot(char *name) {
+ {
+ struct timespec ts;
+ if(clock_gettime(CLOCK_REALTIME, &ts) < 0) {
+ fprintf(stderr, "clock_gettime(CLOCK_REALTIME): %m\n");
+ abort();
+ }
+ sprintf(name, "%lld", (long long)ts.tv_sec);
+ }
+
+ if(mkdirat(backup_dfd, name, 0700) < 0) {
+ fprintf(stderr, "Failed to create $PGBAK/%s: %m\n", name);
+ return -1;
+ }
+
+ int subdfd = openat(backup_dfd, name, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ if(subdfd < 0) {
+ fprintf(stderr, "Failed to open $PGBAK/%s: %m\n", name);
+ goto fail_rmdir;
+ }
+
+ if(mkdirat(subdfd, "pg_wal", 0700) < 0) {
+ fprintf(stderr, "Failed to create $PGBAK/%s/pg_wal: %m\n", name);
+ goto fail_close;
+ }
+
+ int out_fd = -1;
+ out_fd = openat(subdfd, ".", O_WRONLY | O_TMPFILE | O_CLOEXEC, 0600);
+ if(out_fd < 0) {
+ fprintf(stderr, "Failed to create $PGBAK/%s/%s: %m\n", name, BASE_OUT);
+ goto fail_clean;
+ }
+
+ (void)unlinkat(backup_dfd, "current", 0);
+ if(symlinkat(name, backup_dfd, "current") < 0) {
+ fprintf(stderr, "Failed to update $PGBAK/current: %m\n");
+ goto fail;
+ }
+
+ int pfd[2];
+ if(pipe(pfd) < 0) {
+ fprintf(stderr, "pipe(): %m\n");
+ goto fail;
+ }
+
+ fprintf(stderr, "Creating full backup in $PGBAK/%s/%s\n", name, BASE_OUT);
+
+ pid_t pid_backup = cld_spawn(-1, pfd[1], -1, BASE_BACKUP_ARGV);
+ close(pfd[1]);
+
+ if(cld_pipe(pfd[0], out_fd, BASE_COMPRESS_ARGV)) {
+ (void)kill(pid_backup, SIGKILL);
+ (void)waitpid(pid_backup, NULL, 0);
+ goto fail;
+ }
+ if(cld_wait(pid_backup, BASE_BACKUP_ARGV[0])) {
+ goto fail;
+ }
+
+ char fd_path[32];
+ sprintf(fd_path, "/proc/self/fd/%d", out_fd);
+ if(linkat(AT_FDCWD, fd_path, subdfd, BASE_OUT, AT_SYMLINK_FOLLOW) < 0) {
+ fprintf(stderr, "Failed to link base backup: %m\n");
+ goto fail;
+ }
+
+ close(out_fd);
+ if(fsync(subdfd) < 0 || fsync(backup_dfd) < 0) {
+ fprintf(stderr, "fsync(): %m\n");
+ abort();
+ }
+ return subdfd;
+
+fail:
+ close(out_fd);
+fail_clean:
+ (void)unlinkat(subdfd, "pg_wal", AT_REMOVEDIR);
+fail_close:
+ close(subdfd);
+fail_rmdir:
+ (void)unlinkat(backup_dfd, name, AT_REMOVEDIR);
+ return -1;
+}
+
+static bool should_pgbasebackup(int subdfd) {
+ struct stat st;
+
+ if(fstatat(subdfd, BASE_OUT, &st, AT_SYMLINK_NOFOLLOW) < 0) {
+ fprintf(stderr, "Failed to stat %s: %m\n", BASE_OUT);
+ return true;
+ }
+ if(!S_ISREG(st.st_mode)) {
+ fprintf(stderr, "Expected regular file at %s\n", BASE_OUT);
+ return true;
+ }
+
+ off_t base_size = st.st_size;
+ off_t wal_size = 0;
+ off_t wal_count = 0;
+
+ int wal_dfd = openat(subdfd, "pg_wal", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ if(wal_dfd < 0) {
+ fprintf(stderr, "Failed to open $PGBAK/current/pg_wal: %m\n");
+ return true;
+ }
+
+ DIR *wal_dir = fdopendir(wal_dfd);
+ if(!wal_dir) {
+ fprintf(stderr, "fdopendir(): %m\n");
+ abort();
+ }
+
+ while(true) {
+ errno = 0;
+ struct dirent *ent = readdir(wal_dir);
+ if(!ent) {
+ if(errno == 0) break;
+ fprintf(stderr, "readdir(): %m\n");
+ abort();
+ }
+ if(!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, "..")) continue;
+
+ wal_count += 1;
+ if(fstatat(wal_dfd, ent->d_name, &st, AT_SYMLINK_NOFOLLOW) < 0) continue;
+ wal_size += st.st_size;
+ }
+ closedir(wal_dir);
+
+ return wal_count > 8 && (wal_size >> 1) >= base_size;
+}
+
+// Should we become an archiver? If so, acquire `backup` and `wait` locks.
+static bool bak_begin(bool force) {
+ bool r = false;
+ lck_wait(0);
+
+ if(!lck_try(1)) {
+ if(force) lck_write(0, 2);
+ goto end;
+ }
+
+ if(!force && lck_read(0) <= 0) {
+ lck_release(1);
+ goto end;
+ }
+
+ lck_wait(2);
+ r = true;
+
+end:
+ lck_release(0);
+ return r;
+}
+
+// Archiver
+static void bak_work(void) {
+ unsigned int backoff = 4 * 512;
+ char name[32];
+ char ts_s[32];
+ const char *const cmd[] = {
+ "../scripts/backup", name, ts_s, NULL,
+ };
+
+ int subdfd = -1;
+
+ {
+ ssize_t r = readlinkat(backup_dfd, "current", name, sizeof(name));
+ if(r < 0) {
+ if(errno != ENOENT) {
+ fprintf(stderr, "Failed to readlink() $PGBAK/current: %m\n");
+ exit(1);
+ }
+ } else if((size_t)r >= sizeof(name)) {
+ fprintf(stderr, "Symlink $PGBAK/current target too long\n");
+ exit(1);
+ } else {
+ name[r] = 0;
+ subdfd = openat(backup_dfd, name, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ }
+ }
+
+ bool want_ts = true;
+ while(true) {
+ lck_write(0, 1);
+
+ bool want_snapshot = false;
+ const char *failed = NULL;
+ if(subdfd >= 0) {
+ if(want_ts) {
+ struct timespec ts;
+ if(clock_gettime(CLOCK_REALTIME, &ts) < 0) {
+ fprintf(stderr, "clock_gettime(CLOCK_REALTIME): %m\n");
+ abort();
+ }
+ sprintf(ts_s, "%lld", (long long)ts.tv_sec);
+ want_ts = false;
+ }
+
+ pid_t child = cld_spawn(-1, -1, subdfd, cmd);
+ if(cld_wait(child, cmd[0])) {
+ failed = "backup script";
+ } else {
+ fprintf(stderr, "Finished backup %s-%s\n", name, ts_s);
+ }
+
+ if(should_pgbasebackup(subdfd)) {
+ close(subdfd);
+ want_snapshot = true;
+ }
+ } else {
+ want_snapshot = true;
+ }
+
+ if(want_snapshot) {
+ subdfd = bak_snapshot(name);
+ if(subdfd < 0) {
+ failed = "pg_basebackup";
+ }
+ }
+
+ lck_wait(0);
+ int r = lck_read(0);
+ if(r < 0) {
+ fprintf(stderr, "Lock file truncated: %m\n");
+ abort();
+ }
+ if(r > 1) {
+ want_ts = true;
+ } else if(!failed) {
+ lck_write(0, 0);
+ break;
+ }
+ lck_release(0);
+
+ if(failed) {
+ backoff += backoff >> 2;
+ if(backoff > 153600) backoff = 153600;
+ unsigned rnd;
+ (void)getentropy(&rnd, sizeof(rnd));
+ backoff += rnd & 1023;
+
+ struct timespec tv = {
+ .tv_sec = backoff / 512,
+ .tv_nsec = backoff % 512 * 1953125,
+ };
+ fprintf(stderr, "Error in %s, retrying in %u.%09u seconds\n", failed, (unsigned)tv.tv_sec, (unsigned)tv.tv_nsec);
+ (void)nanosleep(&tv, NULL);
+ } else {
+ backoff = 4 * 512;
+ }
+ }
+}
+
+static void on_sigalrm(int) {
+ _Exit(1);
+}
+
+static int cmd_wait(long timeout) {
+ if(timeout == 0) {
+ if(lck_try(2)) return 0;
+ return 1;
+ }
+ if(timeout > 0 && (unsigned long)timeout <= UINT_MAX) {
+ signal(SIGALRM, on_sigalrm);
+ alarm((unsigned)timeout);
+ }
+ lck_wait(2);
+ return 0;
+}
+
+static int cmd_wal(const char *name) {
+ size_t name_len = strlen(name);
+ if(name_len < 8 || name_len >= 192 || !!memcmp(name, "pg_wal/", 7) || memchr(name + 7, '/', name_len - 7)) {
+ fprintf(stderr, "Invalid WAL file name '%s'\n", name);
+ return 1;
+ }
+
+ int wal_dfd = openat(backup_dfd, "current/pg_wal", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ if(wal_dfd < 0) {
+ if(errno == ENOENT) goto do_full;
+ fprintf(stderr, "Failed to open $PGBAK/current/pg_wal: %m\n");
+ return 1;
+ }
+
+ char name_out[256];
+ memcpy(name_out, name + 7, name_len - 7);
+ memcpy(name_out + name_len - 7, WAL_EXT, strlen(WAL_EXT) + 1);
+
+ if(faccessat(wal_dfd, name_out, R_OK, AT_SYMLINK_NOFOLLOW) >= 0) {
+ fprintf(stderr, "WAL backup exists at $PGBAK/current/%s, skipping\n", name_out);
+ return 0;
+ }
+
+ int out_fd = openat(wal_dfd, ".", O_WRONLY | O_TMPFILE | O_CLOEXEC, 0600);
+ if(out_fd < 0) {
+ fprintf(stderr, "Failed to create WAL backup file at $PGBAK/current: %m\n");
+ goto fail_dir;
+ }
+
+ int in_fd = open(name, O_RDONLY | O_CLOEXEC);
+ if(in_fd < 0) {
+ fprintf(stderr, "Failed to open WAL file %s: %m\n", name);
+ goto fail;
+ }
+
+ fprintf(stderr, "Archiving %s\n", name);
+
+ if(cld_pipe(in_fd, out_fd, WAL_COMPRESS_ARGV)) {
+ fprintf(stderr, "Failed to create WAL backup\n");
+ goto fail;
+ }
+
+ char fd_path[32];
+ sprintf(fd_path, "/proc/self/fd/%d", out_fd);
+ if(linkat(AT_FDCWD, fd_path, wal_dfd, name_out, AT_SYMLINK_FOLLOW) < 0) {
+ fprintf(stderr, "Failed to link WAL backup: %m\n");
+ goto fail;
+ }
+ close(out_fd);
+
+ if(fsync(wal_dfd) < 0) {
+ fprintf(stderr, "fsync(): %m\n");
+ goto fail_dir;
+ }
+ close(wal_dfd);
+
+do_full:
+ if(!bak_begin(true)) return 0;
+
+ pid_t r = fork();
+ if(r < 0) {
+ fprintf(stderr, "fork(): %m\n");
+ abort();
+ }
+ if(r != 0) return 0;
+
+ bak_work();
+ exit(0);
+
+fail:
+ close(out_fd);
+fail_dir:
+ close(wal_dfd);
+ return 1;
+}
+
+int main(int argc, char **argv) {
+ if(argc == 1) goto usage;
+
+ const char *backup_dir = getenv("PGBAK");
+ if(!backup_dir || backup_dir[0] != '/') {
+ fprintf(stderr, "$PGBAK not set to an absolute path\n");
+ return 1;
+ }
+
+ backup_dfd = open(backup_dir, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ if(backup_dfd < 0) {
+ fprintf(stderr, "Failed to open $PGBAK directory '%s': %m\n", backup_dir);
+ return 1;
+ }
+
+ lck_fd = openat(backup_dfd, "pgbak.lock", O_RDWR | O_CREAT | O_CLOEXEC, 0600);
+ if(lck_fd < 0) {
+ fprintf(stderr, "Failed to open $PGBAK/pgbak.lock: %m\n");
+ return 1;
+ }
+
+ const char *op = argv[1];
+
+ if(!strcmp(op, "wal")) {
+ if(argc != 3) goto usage;
+ return cmd_wal(argv[2]);
+ }
+
+ if(!strcmp(op, "sync")) {
+ if(argc != 2) goto usage;
+ if(bak_begin(false)) {
+ bak_work();
+ return 0;
+ }
+ return cmd_wait(-1);
+ }
+
+ if(!strcmp(op, "force-sync")) {
+ if(argc != 2) goto usage;
+ if(bak_begin(true)) {
+ bak_work();
+ return 0;
+ }
+ return cmd_wait(-1);
+ }
+
+ if(!strcmp(op, "wait")) {
+ if(argc != 2 && argc != 3) goto usage;
+ long timeout = -1;
+ if(argc > 2) {
+ char *ep = NULL;
+ timeout = strtol(argv[2], &ep, 10);
+ if(timeout < 0 || ep == argv[2] || *ep != 0) goto usage;
+ }
+ return cmd_wait(timeout);
+ }
+
+usage:
+ char *arg0 = argv[0];
+ fprintf(stderr, "Usage:\n\t%s wal PATH\n\t%s sync\n\t%s force-sync\n\t%s wait [TIMEOUT_SEC]\n", arg0, arg0, arg0, arg0);
+ return 1;
+}
diff --git a/test.py b/test.py
new file mode 100644
index 0000000..b67d26c
--- /dev/null
+++ b/test.py
@@ -0,0 +1,187 @@
+import os
+import random
+import re
+import select
+import shlex
+import shutil
+import socket
+import subprocess
+import tarfile
+import tempfile
+import threading
+import time
+import unittest
+
+def unzst(data):
+ return subprocess.run(['zstd', '-d'], stdout=subprocess.PIPE, input=data).stdout
+
+class Test(unittest.TestCase):
+ def setUp(self):
+ self._done = False
+
+ self._wal_lock = threading.Lock()
+ self._wal_k = -1
+ self._wal_i = 0
+ self._wal_req = threading.Condition(self._wal_lock)
+ self._wal_done = threading.Condition(self._wal_lock)
+
+ self._bak_relax = False
+ self._bak_list = []
+
+ self._prog = os.path.realpath('./pgbak')
+ self._sock,self._sock_prog = socket.socketpair(socket.AF_UNIX)
+
+ self._tmpdir = tempfile.mkdtemp()
+ self._bin_path = os.path.join(self._tmpdir, 'bin')
+ os.mkdir(self._bin_path)
+ self._bak_path = os.path.join(self._tmpdir, 'bak')
+ os.mkdir(self._bak_path)
+ os.mkdir(os.path.join(self._bak_path, 'scripts'))
+ self._db_path = os.path.join(self._tmpdir, 'db')
+ os.mkdir(self._db_path)
+ os.mkdir(os.path.join(self._db_path, 'pg_wal'))
+
+ with open(os.path.join(self._bin_path, 'pg_basebackup'), 'w') as f:
+ f.write('#!/bin/sh\necho -n r >&0; read t; cat base; sleep "$t"; [ "$((RANDOM%200))" != 0 ]\n')
+ os.fchmod(f.fileno(), 0o755)
+
+ with open(os.path.join(self._bak_path, 'scripts', 'backup'), 'w') as f:
+ shp = shlex.quote(self._tmpdir)
+ f.write(f'#!/bin/sh\nset -e; sleep 0.1; [ "$((RANDOM%200))" == 0 ] && exit 1; tar -c . > {shp}/bak-dir.tar; echo -n w >&0; read t\n')
+ os.fchmod(f.fileno(), 0o755)
+
+ self._wal_thr = threading.Thread(target=self._run_wal)
+ self._sock_thr = threading.Thread(target=self._run_sock)
+
+ self._wal_thr.start()
+ self._sock_thr.start()
+
+ self._wal_wait(-1)
+
+ def _run_wal(self):
+ i = 0
+ while True:
+ with open(os.path.join(self._db_path, 'pg_wal', f'{i}'), 'wb') as f:
+ f.write(f'wal {i}\n'.encode() + os.urandom(4096))
+
+ with self._wal_lock:
+ self._wal_k = i
+ self._wal_done.notify_all()
+ while self._wal_i == i:
+ self._wal_req.wait()
+ if self._done:
+ return
+
+ time.sleep(random.random() * 0.2)
+ self._run('wal', f'pg_wal/{i}')
+ i += 1
+
+ def _run_sock(self):
+ while True:
+ op = self._sock.recv(1)
+ if not op:
+ break
+
+ if op == b'w':
+ self._bak_read()
+ self._sock.send(b'.\n')
+ continue
+
+ if op == b'r':
+ i = self._wal_make()
+ with open(os.path.join(self._db_path, 'base'), 'wb') as f:
+ f.write(f'up to {i}\n'.encode() + os.urandom(20480))
+ t = random.random() * 0.2
+ self._wal_make()
+ self._sock.send(f'{t}\n'.encode())
+ continue
+
+ raise RuntimeError(f'bad command {op!r}')
+
+ def _wal_wait(self, i):
+ with self._wal_lock:
+ while self._wal_k <= i:
+ self._wal_done.wait()
+
+ def _wal_gen(self):
+ with self._wal_lock:
+ self._wal_i = (i := self._wal_i) + 1
+ self._wal_req.notify()
+ return i
+
+ def tearDown(self):
+ with self._wal_lock:
+ self._done = True
+ self._wal_req.notify()
+ self._sock_prog.close()
+
+ self._wal_thr.join()
+ self._sock_thr.join()
+
+ self._sock.close()
+ shutil.rmtree(self._tmpdir)
+
+ def _wal_make(self):
+ i = self._wal_gen()
+ self._wal_wait(i)
+ return i
+
+ def _bak_read(self):
+ with tarfile.TarFile(os.path.join(self._tmpdir, 'bak-dir.tar')) as tf:
+ data = unzst(tf.extractfile('./base.tzst').read()).split(b'\n')[0].decode()
+ m = re.fullmatch('up to ([0-9]+)', data)
+ if m is None:
+ raise ValueError(f'bad base data')
+ begin = int(m.group(1))
+
+ wals = set()
+ for i in tf.getmembers():
+ if i.name in {'.', './base.tzst', './pg_wal'}:
+ continue
+ m = re.fullmatch('\./pg_wal/(0|[1-9][0-9]*)\.zst', i.name)
+ if m is None:
+ raise ValueError(f'bad archive member {i.name!r}')
+ data = unzst(tf.extractfile(i).read()).split(b'\n')[0].decode()
+ m = re.fullmatch('wal ([0-9]+)', data)
+ if m is None:
+ raise ValueError(f'bad WAL data in {i.name!r}')
+ wals.add(int(m.group(1)))
+
+ print('>>> got backup', begin,sorted(wals))
+
+ end = begin
+ while end in wals:
+ end += 1
+ end -= 1
+ if end < begin + 1 and not self._bak_relax:
+ raise RuntimeError('missing first WAL')
+
+ self._bak_list.append(end)
+
+ def _run(self, *args):
+ env = {**os.environ}
+ env['PATH'] = f"{self._bin_path}:{env['PATH']}"
+ env['PGBAK'] = self._bak_path
+ subprocess.run([self._prog, *args], env=env, cwd=self._db_path, stdin=self._sock_prog, check=True)
+
+ def testArchiving(self):
+ for _ in range(1000):
+ i = self._wal_make()
+ if random.randrange(20) == 0:
+ self._run('wait')
+ if not self._bak_relax:
+ self.assertGreaterEqual(self._bak_list[-1], i)
+ self._bak_relax = False
+
+ if random.randrange(30) == 0:
+ # Relax the backup consistency requirement until the end of the next sync
+ self._bak_relax = True
+ try:
+ os.unlink(os.path.join(self._bak_path, 'current'))
+ except FileNotFoundError:
+ pass
+ else:
+ print('>>> forcing full backup')
+
+if __name__ == '__main__':
+ unittest.main()