importd: automatically grow /var/lib/machines/ loopback filesystem during downloads

If /var/lib/machines is mounted as btrfs loopback file system in
/var/lib/machines.raw with this change we automatically grow the file
system as it fills up. After each 10M we write to it during imports, we
check the free disk space, and if the fill level grows beyond 66% we
increase the size of the file system to 3x the fill level (thus lowering
it to 33%).

4 files changed, 91 insertions, 6 deletions

diff --git a/src/shared/btrfs-util.c b/src/shared/btrfs-util.c
index 52fc5f4a17..256c5a6995 100644
--- a/src/shared/btrfs-util.c
+++ b/src/shared/btrfs-util.c
@@ -705,7 +705,7 @@ int btrfs_quota_limit(const char *path, uint64_t referred_max) {
         return btrfs_quota_limit_fd(fd, referred_max);
 }
 
-int btrfs_resize_loopback_fd(int fd, uint64_t new_size) {
+int btrfs_resize_loopback_fd(int fd, uint64_t new_size, bool grow_only) {
         struct btrfs_ioctl_vol_args args = {};
         _cleanup_free_ char *p = NULL, *loop = NULL, *backing = NULL;
         _cleanup_close_ int loop_fd = -1, backing_fd = -1;
@@ -726,6 +726,8 @@ int btrfs_resize_loopback_fd(int fd, uint64_t new_size) {
         if (asprintf(&p, "/sys/dev/block/%u:%u/loop/backing_file", major(dev), minor(dev)) < 0)
                 return -ENOMEM;
         r = read_one_line_file(p, &backing);
+        if (r == -ENOENT)
+                return -ENODEV;
         if (r < 0)
                 return r;
         if (isempty(backing) || !path_is_absolute(backing))
@@ -743,6 +745,9 @@ int btrfs_resize_loopback_fd(int fd, uint64_t new_size) {
         if (new_size == (uint64_t) st.st_size)
                 return 0;
 
+        if (grow_only && new_size < (uint64_t) st.st_size)
+                return -EINVAL;
+
         if (asprintf(&loop, "/dev/block/%u:%u", major(dev), minor(dev)) < 0)
                 return -ENOMEM;
         loop_fd = open(loop, O_RDWR|O_CLOEXEC|O_NOCTTY);
@@ -770,15 +775,19 @@ int btrfs_resize_loopback_fd(int fd, uint64_t new_size) {
                         return -errno;
         }
 
-        return 0;
+        /* Make sure the free disk space is correctly updated for both file systems */
+        (void) fsync(fd);
+        (void) fsync(backing_fd);
+
+        return 1;
 }
 
-int btrfs_resize_loopback(const char *p, uint64_t new_size) {
+int btrfs_resize_loopback(const char *p, uint64_t new_size, bool grow_only) {
         _cleanup_close_ int fd = -1;
 
         fd = open(p, O_RDONLY|O_NOCTTY|O_CLOEXEC);
         if (fd < 0)
                 return -errno;
 
-        return btrfs_resize_loopback_fd(fd, new_size);
+        return btrfs_resize_loopback_fd(fd, new_size, grow_only);
 }
diff --git a/src/shared/btrfs-util.h b/src/shared/btrfs-util.h
index e654a3fea1..a2c246b8d6 100644
--- a/src/shared/btrfs-util.h
+++ b/src/shared/btrfs-util.h
@@ -72,5 +72,5 @@ int btrfs_quota_enable(const char *path, bool b);
 int btrfs_quota_limit_fd(int fd, uint64_t referred_max);
 int btrfs_quota_limit(const char *path, uint64_t referred_max);
 
-int btrfs_resize_loopback_fd(int fd, uint64_t size);
-int btrfs_resize_loopback(const char *path, uint64_t size);
+int btrfs_resize_loopback_fd(int fd, uint64_t size, bool grow_only);
+int btrfs_resize_loopback(const char *path, uint64_t size, bool grow_only);
diff --git a/src/shared/machine-pool.c b/src/shared/machine-pool.c
index b74252dbc8..3eafb9443a 100644
--- a/src/shared/machine-pool.c
+++ b/src/shared/machine-pool.c
@@ -169,6 +169,7 @@ int setup_machine_directory(uint64_t size, sd_bus_error *error) {
         _cleanup_free_ char* loopdev = NULL;
         char tmpdir[] = "/tmp/import-mount.XXXXXX", *mntdir = NULL;
         bool tmpdir_made = false, mntdir_made = false, mntdir_mounted = false;
+        char buf[FORMAT_BYTES_MAX];
         int r, nr = -1;
 
         /* btrfs cannot handle file systems < 16M, hence use this as minimum */
@@ -274,6 +275,10 @@ int setup_machine_directory(uint64_t size, sd_bus_error *error) {
                 goto fail;
         }
 
+        (void) syncfs(fd);
+
+        log_info("Set up /var/lib/machines as btrfs loopback file system of size %s mounted on /var/lib/machines.raw.", format_bytes(buf, sizeof(buf), size));
+
         (void) umount2(mntdir, MNT_DETACH);
         (void) rmdir(mntdir);
         (void) rmdir(tmpdir);
@@ -299,3 +304,73 @@ fail:
 
         return r;
 }
+
+static int sync_path(const char *p) {
+        _cleanup_close_ int fd = -1;
+
+        fd = open(p, O_RDONLY|O_CLOEXEC|O_NOCTTY);
+        if (fd < 0)
+                return -errno;
+
+        if (syncfs(fd) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int grow_machine_directory(void) {
+        char buf[FORMAT_BYTES_MAX];
+        struct statvfs a, b;
+        uint64_t old_size, new_size, max_add;
+        int r;
+
+        /* Ensure the disk space data is accurate */
+        sync_path("/var/lib/machines");
+        sync_path("/var/lib/machines.raw");
+
+        if (statvfs("/var/lib/machines.raw", &a) < 0)
+                return -errno;
+
+        if (statvfs("/var/lib/machines", &b) < 0)
+                return -errno;
+
+        /* Don't grow if not enough disk space is available on the host */
+        if (((uint64_t) a.f_bavail * (uint64_t) a.f_bsize) <= VAR_LIB_MACHINES_FREE_MIN)
+                return 0;
+
+        /* Don't grow if at least 1/3th of the fs is still free */
+        if (b.f_bavail > b.f_blocks / 3)
+                return 0;
+
+        /* Calculate how much we are willing to add at maximum */
+        max_add = ((uint64_t) a.f_bavail * (uint64_t) a.f_bsize) - VAR_LIB_MACHINES_FREE_MIN;
+
+        /* Calculate the old size */
+        old_size = (uint64_t) b.f_blocks * (uint64_t) b.f_bsize;
+
+        /* Calculate the new size as three times the size of what is used right now */
+        new_size = ((uint64_t) b.f_blocks - (uint64_t) b.f_bavail) * (uint64_t) b.f_bsize * 3;
+
+        /* Always, grow at least to the start size */
+        if (new_size < VAR_LIB_MACHINES_SIZE_START)
+                new_size = VAR_LIB_MACHINES_SIZE_START;
+
+        /* If the new size is smaller than the old size, don't grow */
+        if (new_size < old_size)
+                return 0;
+
+        /* Ensure we never add more than the maximum */
+        if (new_size > old_size + max_add)
+                new_size = old_size + max_add;
+
+        r = btrfs_resize_loopback("/var/lib/machines", new_size, true);
+        if (r <= 0)
+                return r;
+
+        r = btrfs_quota_limit("/var/lib/machines", new_size);
+        if (r < 0)
+                return r;
+
+        log_info("Grew /var/lib/machines btrfs loopback file system to %s.", format_bytes(buf, sizeof(buf), new_size));
+        return 1;
+}
diff --git a/src/shared/machine-pool.h b/src/shared/machine-pool.h
index 9c9849f618..06c5d40583 100644
--- a/src/shared/machine-pool.h
+++ b/src/shared/machine-pool.h
@@ -24,3 +24,4 @@
 #include "sd-bus.h"
 
 int setup_machine_directory(uint64_t size, sd_bus_error *error);
+int grow_machine_directory(void);