Re: [PATCH 1/2 v1] blkdrv: Add queue limits parameters for sg block drive

This patch adds some queue limit parameters into block drive. And inits them
for sg block drive. Some interfaces are also added for accessing them.

Signed-off-by: Cong Meng <redacted>
---
 block/raw-posix.c |   58 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 block_int.h       |    4 +++
 blockdev.c        |   15 +++++++++++++
 hw/block-common.h |    3 ++
 4 files changed, 80 insertions(+), 0 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 0dce089..a086f89 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c

@@ -53,6 +53,7 @@
 #include <linux/cdrom.h>
 #include <linux/fd.h>
 #include <linux/fs.h>
+#include <dirent.h>
 #endif
 #ifdef CONFIG_FIEMAP
 #include <linux/fiemap.h>

@@ -829,6 +830,62 @@ static int hdev_probe_device(const char *filename)
     return 0;
 }

+static void read_queue_limit(char *path, const char *filename, unsigned int *val)
+{
+    FILE *f;
+    char *tail = path + strlen(path);
+
+    pstrcat(path, MAXPATHLEN, filename);
+    f = fopen(path, "r");
+    if (!f) {
+        goto out;
+    }
+
+    fscanf(f, "%u", val);
+    fclose(f);
+
+out:
+    *tail = 0;
+}
+
+static void sg_get_queue_limits(BlockDriverState *bs, const char *filename)
+{
+    DIR *ffs;
+    struct dirent *d;
+    char path[MAXPATHLEN];
+
+    snprintf(path, MAXPATHLEN,
+             "/sys/class/scsi_generic/sg%s/device/block/",
+             filename + strlen("/dev/sg"));
+
+    ffs = opendir(path);
+    if (!ffs) {
+        return;
+    }
+
+    for (;;) {
+        d = readdir(ffs);
+        if (!d) {
+            return;

+        }
+
+        if (strcmp(d->d_name, ".") == 0 || strcmp(d->d_name, "..") == 0) {
+            continue;
+        }
+
+        break;
+    }

+
+    closedir(ffs);
+
+    pstrcat(path, MAXPATHLEN, d->d_name);
+    pstrcat(path, MAXPATHLEN, "/queue/");
+
+    read_queue_limit(path, "max_sectors_kb", &bs->max_sectors);
+    read_queue_limit(path, "max_segments", &bs->max_segments);
+    read_queue_limit(path, "max_segment_size", &bs->max_segment_size);
+}
+
 static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
 {
     BDRVRawState *s = bs->opaque;

@@ -868,6 +925,7 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
         temp = realpath(filename, resolved_path);
         if (temp && strstart(temp, "/dev/sg", NULL)) {
             bs->sg = 1;
+            sg_get_queue_limits(bs, temp);
         }
     }
 #endif

diff --git a/block_int.h b/block_int.h
index d72317f..a9d07a2 100644
--- a/block_int.h
+++ b/block_int.h

@@ -333,6 +333,10 @@ struct BlockDriverState {

     /* long-running background operation */
     BlockJob *job;
+
+    unsigned int max_sectors;
+    unsigned int max_segments;
+    unsigned int max_segment_size;
 };

 int get_tmp_filename(char *filename, int size);

diff --git a/blockdev.c b/blockdev.c
index 3d75015..e17edbf 100644
--- a/blockdev.c
+++ b/blockdev.c

@@ -1191,3 +1191,18 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
     bdrv_iterate(do_qmp_query_block_jobs_one, &prev);
     return dummy.next;
 }
+
+unsigned int get_queue_max_sectors(BlockDriverState *bs)