[Qemu-devel] [PATCH v4] block: more read-only changes, related to backing files

[Naphtali Sprei <nsprei@redhat.com>]

This version includes handling the case the backing file cannot be re-opened


Open backing file read-only where possible
Upgrade backing file to read-write during commit, back to read-only after commit
  If upgrade fail, back to read-only. If also fail, "disconnect" the drive.
Added option for qemu-img.c bdrv_new_open() to open file as read-only

Signed-off-by: Naphtali Sprei <nsprei@redhat.com>
---
 block.c     |   80 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
 block_int.h |    2 +
 qemu-img.c  |   15 +++++++---
 3 files changed, 82 insertions(+), 15 deletions(-)

diff --git a/block.c b/block.c
index 1919d19..612a24b 100644
--- a/block.c
+++ b/block.c
@@ -363,6 +363,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
     bs->is_temporary = 0;
     bs->encrypted = 0;
     bs->valid_key = 0;
+    bs->open_flags = flags;
     /* buffer_alignment defaulted to 512, drivers can change this value */
     bs->buffer_alignment = 512;
 
@@ -450,7 +451,6 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
     if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
         bs->enable_write_cache = 1;
 
-    bs->read_only = (flags & BDRV_O_RDWR) == 0;
     if (!(flags & BDRV_O_FILE)) {
         open_flags = (flags & (BDRV_O_RDWR | BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
         if (bs->is_temporary) { /* snapshot should be writeable */
@@ -465,6 +465,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
         goto free_and_fail;
     }
 
+    bs->keep_read_only = bs->read_only = !(open_flags & BDRV_O_RDWR);
     if (drv->bdrv_getlength) {
         bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
     }
@@ -481,13 +482,22 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
                      filename, bs->backing_file);
         if (bs->backing_format[0] != '\0')
             back_drv = bdrv_find_format(bs->backing_format);
+
+        /* backing files always opened read-only */
+        open_flags &= ~BDRV_O_RDWR;
+        
         ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
                          back_drv);
-        bs->backing_hd->read_only =  (open_flags & BDRV_O_RDWR) == 0;
         if (ret < 0) {
             bdrv_close(bs);
             return ret;
         }
+        if (bs->is_temporary) {
+            bs->backing_hd->keep_read_only = !(flags & BDRV_O_RDWR);
+        } else {
+            /* base image inherits from "parent" */
+            bs->backing_hd->keep_read_only = bs->keep_read_only;
+        }
     }
 
     if (!bdrv_key_required(bs)) {
@@ -563,19 +573,48 @@ int bdrv_commit(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     int64_t i, total_sectors;
-    int n, j;
-    int ret = 0;
+    int n, j, ro, open_flags;
+    int ret = 0, rw_ret = 0;
     unsigned char sector[512];
+    char filename[1024];
+    BlockDriverState *bs_rw, *bs_ro;
 
     if (!drv)
         return -ENOMEDIUM;
+    
+    if (!bs->backing_hd) {
+	return -ENOTSUP;
+    }
 
-    if (bs->read_only) {
+    if (bs->backing_hd->keep_read_only) {
 	return -EACCES;
     }
-
-    if (!bs->backing_hd) {
-	return -ENOTSUP;
+    
+    ro = bs->backing_hd->read_only;
+    strncpy(filename, bs->backing_hd->filename, sizeof(filename));
+    open_flags =  bs->backing_hd->open_flags;
+
+    if (ro) {
+        /* re-open as RW */
+        bdrv_delete(bs->backing_hd);
+        bs->backing_hd = NULL;
+        bs_rw = bdrv_new("");
+        rw_ret = bdrv_open2(bs_rw, filename, open_flags | BDRV_O_RDWR, NULL);
+        if (rw_ret < 0) {
+            bdrv_delete(bs_rw);
+            /* try to re-open read-only */
+            bs_ro = bdrv_new("");
+            ret = bdrv_open2(bs_ro, filename, open_flags & ~BDRV_O_RDWR, NULL);
+            if (ret < 0) {
+                bdrv_delete(bs_ro);
+                /* drive not functional anymore */
+                bs->drv = NULL;
+                return ret;
+            }
+            bs->backing_hd = bs_ro;
+            return rw_ret;
+        }
+        bs->backing_hd = bs_rw;
     }
 
     total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
@@ -583,11 +622,13 @@ int bdrv_commit(BlockDriverState *bs)
         if (drv->bdrv_is_allocated(bs, i, 65536, &n)) {
             for(j = 0; j < n; j++) {
                 if (bdrv_read(bs, i, sector, 1) != 0) {
-                    return -EIO;
+                    ret = -EIO;
+                    goto ro_cleanup;
                 }
 
                 if (bdrv_write(bs->backing_hd, i, sector, 1) != 0) {
-                    return -EIO;
+                    ret = -EIO;
+                    goto ro_cleanup;
                 }
                 i++;
 	    }
@@ -607,6 +648,25 @@ int bdrv_commit(BlockDriverState *bs)
      */
     if (bs->backing_hd)
         bdrv_flush(bs->backing_hd);
+
+ro_cleanup:
+
+    if (ro) {
+        /* re-open as RO */
+        bdrv_delete(bs->backing_hd);
+        bs->backing_hd = NULL;
+        bs_ro = bdrv_new("");
+        ret = bdrv_open2(bs_ro, filename, open_flags & ~BDRV_O_RDWR, NULL);
+        if (ret < 0) {
+            bdrv_delete(bs_ro);
+            /* drive not functional anymore */
+            bs->drv = NULL;
+            return ret;
+        }
+        bs->backing_hd = bs_ro;
+        bs->backing_hd->keep_read_only = 0;
+    }
+
     return ret;
 }
 
diff --git a/block_int.h b/block_int.h
index a0ebd90..93669da 100644
--- a/block_int.h
+++ b/block_int.h
@@ -130,6 +130,8 @@ struct BlockDriverState {
     int64_t total_sectors; /* if we are reading a disk image, give its
                               size in sectors */
     int read_only; /* if true, the media is read only */
+    int keep_read_only; /* if true, the media was requested to stay read only */
+    int open_flags; /* flags used to open the file, re-used for re-open */
     int removable; /* if true, the media can be removed */
     int locked;    /* if true, the media cannot temporarily be ejected */
     int encrypted; /* if true, the media is encrypted */
diff --git a/qemu-img.c b/qemu-img.c
index eb5c0f0..d7b5c23 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -189,11 +189,13 @@ static int read_password(char *buf, int buf_size)
 #endif
 
 static BlockDriverState *bdrv_new_open(const char *filename,
-                                       const char *fmt)
+                                       const char *fmt,
+                                       int readonly)
 {
     BlockDriverState *bs;
     BlockDriver *drv;
     char password[256];
+    int flags = BRDV_O_FLAGS;
 
     bs = bdrv_new("");
     if (!bs)
@@ -205,7 +207,10 @@ static BlockDriverState *bdrv_new_open(const char *filename,
     } else {
         drv = NULL;
     }
-    if (bdrv_open2(bs, filename, BRDV_O_FLAGS | BDRV_O_RDWR, drv) < 0) {
+    if (!readonly) {
+        flags |= BDRV_O_RDWR;
+    }
+    if (bdrv_open2(bs, filename, flags, drv) < 0) {
         error("Could not open '%s'", filename);
     }
     if (bdrv_is_encrypted(bs)) {
@@ -344,7 +349,7 @@ static int img_create(int argc, char **argv)
                 }
             }
 
-            bs = bdrv_new_open(backing_file->value.s, fmt);
+            bs = bdrv_new_open(backing_file->value.s, fmt, 1);
             bdrv_get_geometry(bs, &size);
             size *= 512;
             bdrv_delete(bs);
@@ -628,7 +633,7 @@ static int img_convert(int argc, char **argv)
 
     total_sectors = 0;
     for (bs_i = 0; bs_i < bs_n; bs_i++) {
-        bs[bs_i] = bdrv_new_open(argv[optind + bs_i], fmt);
+        bs[bs_i] = bdrv_new_open(argv[optind + bs_i], fmt, 1);
         if (!bs[bs_i])
             error("Could not open '%s'", argv[optind + bs_i]);
         bdrv_get_geometry(bs[bs_i], &bs_sectors);
@@ -686,7 +691,7 @@ static int img_convert(int argc, char **argv)
         }
     }
 
-    out_bs = bdrv_new_open(out_filename, out_fmt);
+    out_bs = bdrv_new_open(out_filename, out_fmt, 0);
 
     bs_i = 0;
     bs_offset = 0;
-- 
1.6.3.3