[Qemu-block] [PATCH v3 1/3] block: introducing 'bdrv_co_delete_file' interface

[Daniel Henrique Barboza]

Adding to Block Drivers the capability of being able to clean up
its created files can be useful in certain situations. For the
LUKS driver, for instance, a failure in one of its authentication
steps can leave files in the host that weren't there before.

This patch adds the 'bdrv_co_delete_file' interface to block
drivers and add it to the 'file' driver in file-posix.c. The
implementation is given by 'raw_co_delete_file'. The helper
'bdrv_path_is_regular_file' is being used only in raw_co_delete_file
at this moment, but it will be used inside LUKS in a later patch.
Foreseeing this future use, let's put it in block.c and make it
public.

Suggested-by: Daniel P. Berrangé <address@hidden>
Signed-off-by: Daniel Henrique Barboza <address@hidden>
---
 block.c                   | 11 +++++++++++
 block/file-posix.c        | 28 ++++++++++++++++++++++++++++
 include/block/block.h     |  1 +
 include/block/block_int.h |  6 ++++++
 4 files changed, 46 insertions(+)

diff --git a/block.c b/block.c
index 0a93ee9ac8..227362b282 100644
--- a/block.c
+++ b/block.c
@@ -621,6 +621,17 @@ int get_tmp_filename(char *filename, int size)
 #endif
 }
 
+/**
+ * Helper that checks if a given string represents a regular
+ * local file.
+ */
+bool bdrv_path_is_regular_file(const char *path)
+{
+    struct stat st;
+
+    return (stat(path, &st) == 0) && S_ISREG(st.st_mode);
+}
+
 /*
  * Detect host devices. By convention, /dev/cdrom[N] is always
  * recognized as a host CDROM.
diff --git a/block/file-posix.c b/block/file-posix.c
index d102f3b222..09d84bab37 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2342,6 +2342,33 @@ static int coroutine_fn raw_co_create_opts(const char 
*filename, QemuOpts *opts,
     return raw_co_create(&options, errp);
 }
 
+/**
+ * Co-routine function that erases a regular file.
+ */
+static int coroutine_fn raw_co_delete_file(const char *filename,
+                                           Error **errp)
+{
+    int ret;
+
+    /* Skip file: protocol prefix */
+    strstart(filename, "file:", &filename);
+
+    if (!bdrv_path_is_regular_file(filename)) {
+        ret = -ENOENT;
+        error_setg_errno(errp, -ret, "%s is not a regular file", filename);
+        goto done;
+    }
+
+    ret = unlink(filename);
+    if (ret < 0) {
+        ret = -errno;
+        error_setg_errno(errp, -ret, "Error when deleting file %s", filename);
+    }
+
+done:
+    return ret;
+}
+
 /*
  * Find allocation range in @bs around offset @start.
  * May change underlying file descriptor's file offset.
@@ -2867,6 +2894,7 @@ BlockDriver bdrv_file = {
     .bdrv_co_block_status = raw_co_block_status,
     .bdrv_co_invalidate_cache = raw_co_invalidate_cache,
     .bdrv_co_pwrite_zeroes = raw_co_pwrite_zeroes,
+    .bdrv_co_delete_file = raw_co_delete_file,
 
     .bdrv_co_preadv         = raw_co_preadv,
     .bdrv_co_pwritev        = raw_co_pwritev,
diff --git a/include/block/block.h b/include/block/block.h
index e452988b66..820643f96d 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -363,6 +363,7 @@ int bdrv_freeze_backing_chain(BlockDriverState *bs, 
BlockDriverState *base,
                               Error **errp);
 void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base);
 
+bool bdrv_path_is_regular_file(const char *path);
 
 typedef struct BdrvCheckResult {
     int corruptions;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 01e855a066..74abb78ce7 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -309,6 +309,12 @@ struct BlockDriver {
      */
     int coroutine_fn (*bdrv_co_flush)(BlockDriverState *bs);
 
+    /*
+     * Delete a local created file.
+     */
+    int coroutine_fn (*bdrv_co_delete_file)(const char *filename,
+                                            Error **errp);
+
     /*
      * Flushes all data that was already written to the OS all the way down to
      * the disk (for example file-posix.c calls fsync()).
-- 
2.20.1