[RFC v4 3/9] file-posix: introduce get_sysfs_long_val for a block queue of sysfs attribute

[Sam Li <faithilikerun@gmail.com>]

Use sysfs attribute files to get the zoned device information in case
that ioctl() commands of zone management interface won't work.

Signed-off-by: Sam Li <faithilikerun@gmail.com>
---
 block/file-posix.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index e7523ae2ed..3161d39ea4 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1218,15 +1218,19 @@ static int hdev_get_max_hw_transfer(int fd, struct stat *st)
 #endif
 }
 
-static int hdev_get_max_segments(int fd, struct stat *st)
-{
+/*
+ * Get zoned device information (chunk_sectors, zoned_append_max_bytes,
+ * max_open_zones, max_active_zones) through sysfs attribute files.
+ */
+static long get_sysfs_long_val(int fd, struct stat *st,
+                               const char *attribute) {
 #ifdef CONFIG_LINUX
     char buf[32];
     const char *end;
     char *sysfspath = NULL;
     int ret;
     int sysfd = -1;
-    long max_segments;
+    long val;
 
     if (S_ISCHR(st->st_mode)) {
         if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
@@ -1239,8 +1243,9 @@ static int hdev_get_max_segments(int fd, struct stat *st)
         return -ENOTSUP;
     }
 
-    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
-                                major(st->st_rdev), minor(st->st_rdev));
+    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
+                                major(st->st_rdev), minor(st->st_rdev),
+                                attribute);
     sysfd = open(sysfspath, O_RDONLY);
     if (sysfd == -1) {
         ret = -errno;
@@ -1258,9 +1263,9 @@ static int hdev_get_max_segments(int fd, struct stat *st)
     }
     buf[ret] = 0;
     /* The file is ended with '\n', pass 'end' to accept that. */
-    ret = qemu_strtol(buf, &end, 10, &max_segments);
+    ret = qemu_strtol(buf, &end, 10, &val);
     if (ret == 0 && end && *end == '\n') {
-        ret = max_segments;
+        ret = val;
     }
 
 out:
@@ -1274,6 +1279,10 @@ out:
 #endif
 }
 
+static int hdev_get_max_segments(int fd, struct stat *st) {
+    return get_sysfs_long_val(fd, st, "max_segments");
+}
+
 static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
 {
     BDRVRawState *s = bs->opaque;
@@ -1883,10 +1892,17 @@ static int handle_aiocb_zone_mgmt(void *opaque) {
     int64_t zone_size_mask;
     int ret;
 
-    g_autofree struct stat *file = NULL;
-    file = g_new(struct stat, 1);
-    stat(s->filename, file);
-    zone_size = get_sysfs_long_val(fd, file, "chunk_sectors");
+    struct stat file;
+    if (fstat(fd, &file) < 0) {
+        return -errno;
+    }
+    mod = get_sysfs_str_val(fd, &file);
+    if (mod != BLK_Z_HM) {
+        ret = -ENOTSUP;
+        return ret;
+    }
+
+    zone_size = get_sysfs_long_val(fd, &file, "chunk_sectors");
     zone_size_mask = zone_size - 1;
     if (offset & zone_size_mask) {
         error_report("offset is not the start of a zone");
-- 
2.36.1