libext2fs: use ZERO_RANGE before PUNCH_HOLE in unix_zeroout

In unix_zeroout() for files, we should try a ZERO_RANGE before we try
PUNCH_HOLE because the former will not cause us to lose preallocated
blocks.  Since block devices have supported fallocate for a few years
now, refactor the fallocate calls into a helper and call it from either
case.

Reported-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 7a4c9bf..74fc8a7 100644 (file)
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -1126,6 +1126,31 @@ unimplemented:
        return EXT2_ET_UNIMPLEMENTED;
 }
 
+/*
+ * If we know about ZERO_RANGE, try that before we try PUNCH_HOLE because
+ * ZERO_RANGE doesn't unmap preallocated blocks.  We prefer fallocate because
+ * it always invalidates page cache, and libext2fs requires that reads after
+ * ZERO_RANGE return zeroes.
+ */
+static int __unix_zeroout(int fd, off_t offset, off_t len)
+{
+       int ret = -1;
+
+#if defined(HAVE_FALLOCATE) && defined(FALLOC_FL_ZERO_RANGE)
+       ret = fallocate(fd, FALLOC_FL_ZERO_RANGE, offset, len);
+       if (ret == 0)
+               return 0;
+#endif
+#if defined(HAVE_FALLOCATE) && defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)
+       ret = fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+                       offset,  len);
+       if (ret == 0)
+               return 0;
+#endif
+       errno = EOPNOTSUPP;
+       return ret;
+}
+
 /* parameters might not be used if OS doesn't support zeroout */
 #if __GNUC_PREREQ (4, 6)
 #pragma GCC diagnostic push
@@ -1144,10 +1169,7 @@ static errcode_t unix_zeroout(io_channel channel, unsigned long long block,
        if (safe_getenv("UNIX_IO_NOZEROOUT"))
                goto unimplemented;
 
-       if (channel->flags & CHANNEL_FLAGS_BLOCK_DEVICE) {
-               /* Not implemented until the BLKZEROOUT mess is fixed */
-               goto unimplemented;
-       } else {
+       if (!(channel->flags & CHANNEL_FLAGS_BLOCK_DEVICE)) {
                /* Regular file, try to use truncate/punch/zero. */
                struct stat statbuf;
 
@@ -1167,26 +1189,11 @@ static errcode_t unix_zeroout(io_channel channel, unsigned long long block,
                        if (ret)
                                goto err;
                }
-#if defined(HAVE_FALLOCATE) && (defined(FALLOC_FL_ZERO_RANGE) || \
-       (defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)))
-#if defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)
-               ret = fallocate(data->dev,
-                               FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
-                               (off_t)(block) * channel->block_size + data->offset,
-                               (off_t)(count) * channel->block_size);
-               if (ret == 0)
-                       goto err;
-#endif
-#ifdef FALLOC_FL_ZERO_RANGE
-               ret = fallocate(data->dev,
-                               FALLOC_FL_ZERO_RANGE,
-                               (off_t)(block) * channel->block_size + data->offset,
-                               (off_t)(count) * channel->block_size);
-#endif
-#else
-               goto unimplemented;
-#endif /* HAVE_FALLOCATE && (ZERO_RANGE || (PUNCH_HOLE && KEEP_SIZE)) */
        }
+
+       ret = __unix_zeroout(data->dev,
+                       (off_t)(block) * channel->block_size + data->offset,
+                       (off_t)(count) * channel->block_size);
 err:
        if (ret < 0) {
                if (errno == EOPNOTSUPP)