Add a little helper to make /sys/dev/block/major:minor paths

src/basic/btrfs-util.c

@@ -42,6 +42,7 @@
 #include "btrfs-util.h"
 #include "chattr-util.h"
 #include "copy.h"
+#include "device-nodes.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "io-util.h"
@@ -910,7 +911,8 @@ int btrfs_subvol_set_subtree_quota_limit(const char *path, uint64_t subvol_id, u
 
 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;
+        char p[SYS_BLOCK_PATH_MAX("/loop/backing_file")];
+        _cleanup_free_ char *backing = NULL;
         _cleanup_close_ int loop_fd = -1, backing_fd = -1;
         struct stat st;
         dev_t dev = 0;
@@ -930,8 +932,7 @@ int btrfs_resize_loopback_fd(int fd, uint64_t new_size, bool grow_only) {
         if (r == 0)
                 return -ENODEV;
 
-        if (asprintf(&p, "/sys/dev/block/%u:%u/loop/backing_file", major(dev), minor(dev)) < 0)
-                return -ENOMEM;
+        xsprintf_sys_block_path(p, "/loop/backing_file", dev);
         r = read_one_line_file(p, &backing);
         if (r == -ENOENT)
                 return -ENODEV;
@@ -955,9 +956,8 @@ int btrfs_resize_loopback_fd(int fd, uint64_t new_size, bool grow_only) {
         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);
+        xsprintf_sys_block_path(p, NULL, dev);
+        loop_fd = open(p, O_RDWR|O_CLOEXEC|O_NOCTTY);
         if (loop_fd < 0)
                 return -errno;
 

src/basic/device-nodes.h

@@ -23,5 +23,13 @@
 #include <stddef.h>
 #include <sys/types.h>
 
+#include "macro.h"
+#include "stdio-util.h"
+
 int encode_devnode_name(const char *str, char *str_enc, size_t len);
 int whitelisted_char_for_devnode(char c, const char *additional);
+
+#define SYS_BLOCK_PATH_MAX(suffix)                                      \
+        (strlen("/sys/dev/block/") + DECIMAL_STR_MAX(dev_t) + 1 + DECIMAL_STR_MAX(dev_t) + strlen_ptr(suffix))
+#define xsprintf_sys_block_path(buf, suffix, devno)                     \
+        xsprintf(buf, "/sys/dev/block/%u:%u%s", major(devno), minor(devno), strempty(suffix))

src/basic/util.c

@@ -39,6 +39,7 @@
 #include "build.h"
 #include "cgroup-util.h"
 #include "def.h"
+#include "device-nodes.h"
 #include "dirent-util.h"
 #include "fd-util.h"
 #include "fileio.h"
@@ -118,63 +119,42 @@ int socket_from_display(const char *display, char **path) {
 }
 
 int block_get_whole_disk(dev_t d, dev_t *ret) {
-        char *p, *s;
+        char p[SYS_BLOCK_PATH_MAX("/partition")];
+        _cleanup_free_ char *s = NULL;
         int r;
         unsigned n, m;
 
         assert(ret);
 
         /* If it has a queue this is good enough for us */
-        if (asprintf(&p, "/sys/dev/block/%u:%u/queue", major(d), minor(d)) < 0)
-                return -ENOMEM;
-
-        r = access(p, F_OK);
-        free(p);
-
-        if (r >= 0) {
+        xsprintf_sys_block_path(p, "/queue", d);
+        if (access(p, F_OK) >= 0) {
                 *ret = d;
                 return 0;
         }
 
         /* If it is a partition find the originating device */
-        if (asprintf(&p, "/sys/dev/block/%u:%u/partition", major(d), minor(d)) < 0)
-                return -ENOMEM;
-
-        r = access(p, F_OK);
-        free(p);
-
-        if (r < 0)
+        xsprintf_sys_block_path(p, "/partition", d);
+        if (access(p, F_OK) < 0)
                 return -ENOENT;
 
         /* Get parent dev_t */
-        if (asprintf(&p, "/sys/dev/block/%u:%u/../dev", major(d), minor(d)) < 0)
-                return -ENOMEM;
-
+        xsprintf_sys_block_path(p, "/../dev", d);
         r = read_one_line_file(p, &s);
-        free(p);
-
         if (r < 0)
                 return r;
 
         r = sscanf(s, "%u:%u", &m, &n);
-        free(s);
-
         if (r != 2)
                 return -EINVAL;
 
         /* Only return this if it is really good enough for us. */
-        if (asprintf(&p, "/sys/dev/block/%u:%u/queue", m, n) < 0)
-                return -ENOMEM;
+        xsprintf_sys_block_path(p, "/queue", makedev(m, n));
+        if (access(p, F_OK) < 0)
+                return -ENOENT;
 
-        r = access(p, F_OK);
-        free(p);
-
-        if (r >= 0) {
-                *ret = makedev(m, n);
-                return 0;
-        }
-
-        return -ENOENT;
+        *ret = makedev(m, n);
+        return 0;
 }
 
 bool kexec_loaded(void) {
@@ -749,7 +729,8 @@ int get_block_device(const char *path, dev_t *dev) {
 
 int get_block_device_harder(const char *path, dev_t *dev) {
         _cleanup_closedir_ DIR *d = NULL;
-        _cleanup_free_ char *p = NULL, *t = NULL;
+        _cleanup_free_ char *t = NULL;
+        char p[SYS_BLOCK_PATH_MAX("/slaves")];
         struct dirent *de, *found = NULL;
         const char *q;
         unsigned maj, min;
@@ -767,9 +748,7 @@ int get_block_device_harder(const char *path, dev_t *dev) {
         if (r <= 0)
                 return r;
 
-        if (asprintf(&p, "/sys/dev/block/%u:%u/slaves", major(dt), minor(dt)) < 0)
-                return -ENOMEM;
-
+        xsprintf_sys_block_path(p, "/slaves", dt);
         d = opendir(p);
         if (!d) {
                 if (errno == ENOENT)