[Mesa-dev] [PATCH 1/4] util/disk_cache: add support for detecting corrupt cache entries

[Grazvydas Ignotas]

On Wed, Mar 1, 2017 at 7:25 AM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
> ---
>  src/util/disk_cache.c | 37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/src/util/disk_cache.c b/src/util/disk_cache.c
> index f5e1145..2a0edca 100644
> --- a/src/util/disk_cache.c
> +++ b/src/util/disk_cache.c
> @@ -31,20 +31,21 @@
>  #include <sys/file.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <sys/mman.h>
>  #include <unistd.h>
>  #include <fcntl.h>
>  #include <pwd.h>
>  #include <errno.h>
>  #include <dirent.h>
>
> +#include "util/crc32.h"
>  #include "util/u_atomic.h"
>  #include "util/mesa-sha1.h"
>  #include "util/ralloc.h"
>  #include "main/errors.h"
>
>  #include "disk_cache.h"
>
>  /* Number of bits to mask off from a cache key to get an index. */
>  #define CACHE_INDEX_KEY_BITS 16
>
> @@ -702,34 +703,48 @@ disk_cache_put(struct disk_cache *cache,
>     /* OK, we're now on the hook to write out a file that we know is
>      * not in the cache, and is also not being written out to the cache
>      * by some other process.
>      *
>      * Before we do that, if the cache is too large, evict something
>      * else first.
>      */
>     if (*cache->size + size > cache->max_size)
>        evict_random_item(cache);
>
> +   /* Create CRC of the data and store at the start of the file. We will
> +    * read this when restoring the cache and use it to check for corruption.
> +    */
> +   uint32_t crc32 = util_hash_crc32(data, size);
> +   size_t crc_size = sizeof(crc32);
> +   for (len = 0; len < crc_size; len += ret) {
> +      ret = write(fd, &crc32, crc_size - len);

I think you need to advance the data pointer if retrying. There is
also a case of EINTR where you should be retrying on error (ret ==
-1). Might be worth making a helper function.

> +      if (ret == -1) {
> +         unlink(filename_tmp);
> +         goto done;
> +      }
> +   }
> +
>     /* Now, finally, write out the contents to the temporary file, then
>      * rename them atomically to the destination filename, and also
>      * perform an atomic increment of the total cache size.
>      */
>     for (len = 0; len < size; len += ret) {
>        ret = write(fd, p + len, size - len);
>        if (ret == -1) {
>           unlink(filename_tmp);
>           goto done;
>        }
>     }
>
>     rename(filename_tmp, filename);
>
> +   size += crc_size;
>     p_atomic_add(cache->size, size);
>
>   done:
>     if (fd_final != -1)
>        close(fd_final);
>     /* This close finally releases the flock, (now that the final dile
>      * has been renamed into place and the size has been added).
>      */
>     if (fd != -1)
>        close(fd);
> @@ -758,31 +773,47 @@ disk_cache_get(struct disk_cache *cache, cache_key key, size_t *size)
>     if (fd == -1)
>        goto fail;
>
>     if (fstat(fd, &sb) == -1)
>        goto fail;
>
>     data = malloc(sb.st_size);
>     if (data == NULL)
>        goto fail;
>
> -   for (len = 0; len < sb.st_size; len += ret) {
> -      ret = read(fd, data + len, sb.st_size - len);
> +   /* Load the CRC that was created when the file was written. */
> +   uint32_t crc32;
> +   size_t crc_size = sizeof(crc32);
> +   assert(sb.st_size > crc_size);
> +   for (len = 0; len < crc_size; len += ret) {
> +      ret = read(fd, &crc32 + len, crc_size - len);

&crc32 + len doesn't look right, it's a uint32_t * pointer. EINTR
handling is also missing.

Gražvydas