[Qemu-block] [PATCH v2 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 LUKS driver. The implementation is provided
in a new 'bdrv_co_delete_file_generic' function inside block.c. This
function is made public in case other block drivers wants to
support this cleanup interface as well.

Suggested-by: Daniel P. Berrangé <address@hidden>
Signed-off-by: Daniel Henrique Barboza <address@hidden>
---
 block.c                   | 45 +++++++++++++++++++++++++++++++++++++++
 block/crypto.c            |  2 ++
 include/block/block.h     |  3 +++
 include/block/block_int.h |  6 ++++++
 4 files changed, 56 insertions(+)

diff --git a/block.c b/block.c
index 0a93ee9ac8..2b632baba2 100644
--- a/block.c
+++ b/block.c
@@ -547,6 +547,51 @@ int bdrv_create_file(const char *filename, QemuOpts *opts, 
Error **errp)
     return ret;
 }
 
+/**
+ * Helper that checks if a given path 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);
+}
+
+/**
+ * Co-routine function that erases a regular file. Its original
+ * intent is as a implementation of bdrv_co_delete_file for
+ * the "luks" driver that can leave created files behind in the
+ * file system when the authentication fails.
+ *
+ * The function is exposed here, and with 'generic' in its name,
+ * because file removal isn't usually format specific and any other
+ * BlockDriver might want to re-use this function.
+ */
+int coroutine_fn bdrv_co_delete_file_generic(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;
+}
+
 /**
  * Try to get @bs's logical and physical block size.
  * On success, store them in @bsz struct and return 0.
diff --git a/block/crypto.c b/block/crypto.c
index 3af46b805f..c604c96c93 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -639,6 +639,8 @@ static BlockDriver bdrv_crypto_luks = {
     .bdrv_co_truncate   = block_crypto_co_truncate,
     .create_opts        = &block_crypto_create_opts_luks,
 
+    .bdrv_co_delete_file = bdrv_co_delete_file_generic,
+
     .bdrv_reopen_prepare = block_crypto_reopen_prepare,
     .bdrv_refresh_limits = block_crypto_refresh_limits,
     .bdrv_co_preadv     = block_crypto_co_preadv,
diff --git a/include/block/block.h b/include/block/block.h
index e452988b66..efb77daf9f 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -363,6 +363,9 @@ 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);
+int coroutine_fn bdrv_co_delete_file_generic(const char *filename,
+                                             Error **errp);
 
 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