[libvirt] [PATCH v3 1/5] storage: Modify storageBackendWipeLocal to allow zero from end of device

[Michal Privoznik]

On 04/07/2017 06:30 PM, John Ferlan wrote:
> Add bool 'zero_end' and logic that would allow a caller to wipe specific
> portions of a target device either from the beginning (the default) or
> from the end when zero_end is true.
> 
> This will allow for this code to wipe out partition table information
> from a device.
> 
> Signed-off-by: John Ferlan <jferlan at redhat.com>
> ---
>  src/storage/storage_util.c | 48 +++++++++++++++++++++++++++++++++-------------
>  1 file changed, 35 insertions(+), 13 deletions(-)
> 
> diff --git a/src/storage/storage_util.c b/src/storage/storage_util.c
> index a2d89af..c1734e7 100644
> --- a/src/storage/storage_util.c
> +++ b/src/storage/storage_util.c
> @@ -2516,24 +2516,44 @@ static int
>  storageBackendWipeLocal(const char *path,
>                          int fd,
>                          unsigned long long wipe_len,
> -                        size_t writebuf_length)
> +                        size_t writebuf_length,
> +                        bool zero_end)
>  {
>      int ret = -1, written = 0;
>      unsigned long long remaining = 0;
> +    off_t size;
>      size_t write_size = 0;
>      char *writebuf = NULL;
>  
> -    VIR_DEBUG("wiping start: 0 len: %llu", wipe_len);
> -
>      if (VIR_ALLOC_N(writebuf, writebuf_length) < 0)
>          goto cleanup;
>  
> -    if (lseek(fd, 0, SEEK_SET) < 0) {
> -        virReportSystemError(errno,
> -                             _("Failed to seek to the start in volume "
> -                               "with path '%s'"),
> -                             path);
> -        goto cleanup;
> +    if (!zero_end) {
> +        if (lseek(fd, 0, SEEK_SET) < 0) {
> +            virReportSystemError(errno,
> +                                 _("Failed to seek to the start in volume "
> +                                   "with path '%s'"),
> +                                 path);
> +            goto cleanup;
> +        }
> +        VIR_DEBUG("wiping start: 0 len: %llu", wipe_len);
> +    } else {
> +        if ((size = lseek(fd, 0, SEEK_END)) == (off_t)-1) {
> +            virReportSystemError(errno,
> +                                 _("Failed to seek to the end in volume "
> +                                   "with path '%s'"),
> +                                 path);
> +            goto cleanup;
> +        }
> +        size -= wipe_len;
> +        if (lseek(fd, size, SEEK_SET) < 0) {
> +            virReportSystemError(errno,
> +                                 _("Failed to seek to %zd bytes in volume "
> +                                   "with path '%s'"),
> +                                 size, path);

Is off_t really ssize_t? I think we should typecast it.

> +            goto cleanup;
> +        }

Or, instead of these two seeks:

if ((size  = lseek(fd, -wipe_len, SEEK_END)) < 0) {
  virReportSystemError();
  goto cleanup;
}

> +        VIR_DEBUG("wiping start: %zd len: %llu", size, wipe_len);

This DEBUG is the same as in the other body for the if statement. While
it's just VIR_DEBUG I wouldn't care, but just consider the following
for a moment:

Move this VIR_DEBUG right after this if statement and initialize @size
to zero (and obviously drop the other VIR_DEBUG with hardcoded 0). That
way we know what the current position is and how long section is to be
wiped.

Or even better:

+    if (!zero_end) {
+        if ((size = lseek(fd, 0, SEEK_SET)) < 0) {
+            virReportSystemError(errno,
+                                 _("Failed to seek to the start in volume "
+                                   "with path '%s'"),
+                                 path);
+            goto cleanup;
+        }
+    } else {
+        if ((size = lseek(fd, -wipe_len, SEEK_END)) < 0) {
+            virReportSystemError(errno,
+                                 _("Failed to seek to %llu bytes to the end in volume "
+                                   "with path '%s'"),
+                                 wipe_len, path);
+            goto cleanup;
+        }
     }
 
+    VIR_DEBUG("wiping start: %zd len: %llu", (ssize_t) size, wipe_len);


>      }
>  
>      remaining = wipe_len;
> @@ -2573,7 +2593,8 @@ storageBackendWipeLocal(const char *path,
>  static int
>  storageBackendVolWipeLocalFile(const char *path,
>                                 unsigned int algorithm,
> -                               unsigned long long allocation)
> +                               unsigned long long allocation,
> +                               bool zero_end)
>  {
>      int ret = -1, fd = -1;
>      const char *alg_char = NULL;
> @@ -2648,7 +2669,8 @@ storageBackendVolWipeLocalFile(const char *path,
>          if (S_ISREG(st.st_mode) && st.st_blocks < (st.st_size / DEV_BSIZE)) {
>              ret = storageBackendVolZeroSparseFileLocal(path, st.st_size, fd);
>          } else {
> -            ret = storageBackendWipeLocal(path, fd, allocation, st.st_blksize);
> +            ret = storageBackendWipeLocal(path, fd, allocation, st.st_blksize,
> +                                          zero_end);
>          }
>          if (ret < 0)
>              goto cleanup;
> @@ -2686,7 +2708,7 @@ storageBackendVolWipePloop(virStorageVolDefPtr vol,
>          goto cleanup;
>  
>      if (storageBackendVolWipeLocalFile(target_path, algorithm,
> -                                       vol->target.allocation) < 0)
> +                                       vol->target.allocation, false) < 0)
>          goto cleanup;
>  
>      if (virFileRemove(disk_desc, 0, 0) < 0) {
> @@ -2735,7 +2757,7 @@ virStorageBackendVolWipeLocal(virConnectPtr conn ATTRIBUTE_UNUSED,
>          ret = storageBackendVolWipePloop(vol, algorithm);
>      } else {
>          ret = storageBackendVolWipeLocalFile(vol->target.path, algorithm,
> -                                             vol->target.allocation);
> +                                             vol->target.allocation, false);
>      }
>  
>      return ret;
> 

Michal