[RFC PATCH] block/export/fuse: Fix build failure on FreeBSD

[Philippe Mathieu-Daudé]

When building on FreeBSD we get:

  [816/6851] Compiling C object libblockdev.fa.p/block_export_fuse.c.o
  ../block/export/fuse.c:628:16: error: use of undeclared identifier 
'FALLOC_FL_KEEP_SIZE'
      if (mode & FALLOC_FL_KEEP_SIZE) {
                 ^
  ../block/export/fuse.c:632:16: error: use of undeclared identifier 
'FALLOC_FL_PUNCH_HOLE'
      if (mode & FALLOC_FL_PUNCH_HOLE) {
                 ^
  ../block/export/fuse.c:633:22: error: use of undeclared identifier 
'FALLOC_FL_KEEP_SIZE'
          if (!(mode & FALLOC_FL_KEEP_SIZE)) {
                       ^
  3 errors generated.
  FAILED: libblockdev.fa.p/block_export_fuse.c.o

Meson indeed reported FALLOC_FL_PUNCH_HOLE is not available:

  C compiler for the host machine: cc (clang 10.0.1 "FreeBSD clang version 
10.0.1")
  Checking for function "fallocate" : NO
  Checking for function "posix_fallocate" : YES
  Header <linux/falloc.h> has symbol "FALLOC_FL_PUNCH_HOLE" : NO
  Header <linux/falloc.h> has symbol "FALLOC_FL_ZERO_RANGE" : NO
  ...

Similarly to commit 304332039 ("block/export/fuse.c: fix musl build"),
guard the code requiring FALLOC_FL_KEEP_SIZE / FALLOC_FL_PUNCH_HOLE
definitions under CONFIG_FALLOCATE_PUNCH_HOLE #ifdef'ry.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
Fragile #ifdef'ry... Any clever idea?

    ERROR: else should follow close brace '}'
    #17: FILE: block/export/fuse.c:647:
         }
    +    else

    ERROR: else should follow close brace '}'
    #29: FILE: block/export/fuse.c:670:
         }
    +    else

    total: 2 errors, 0 warnings, 28 lines checked
---
 block/export/fuse.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/export/fuse.c b/block/export/fuse.c
index 6710d8aed86..d8bad0e53df 100644
--- a/block/export/fuse.c
+++ b/block/export/fuse.c
@@ -625,6 +625,7 @@ static void fuse_fallocate(fuse_req_t req, fuse_ino_t 
inode, int mode,
         return;
     }
 
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
     if (mode & FALLOC_FL_KEEP_SIZE) {
         length = MIN(length, blk_len - offset);
     }
@@ -643,8 +644,10 @@ static void fuse_fallocate(fuse_req_t req, fuse_ino_t 
inode, int mode,
             length -= size;
         } while (ret == 0 && length > 0);
     }
+    else
+#endif /* CONFIG_FALLOCATE_PUNCH_HOLE */
 #ifdef CONFIG_FALLOCATE_ZERO_RANGE
-    else if (mode & FALLOC_FL_ZERO_RANGE) {
+    if (mode & FALLOC_FL_ZERO_RANGE) {
         if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + length > blk_len) {
             /* No need for zeroes, we are going to write them ourselves */
             ret = fuse_do_truncate(exp, offset + length, false,
@@ -664,8 +667,9 @@ static void fuse_fallocate(fuse_req_t req, fuse_ino_t 
inode, int mode,
             length -= size;
         } while (ret == 0 && length > 0);
     }
+    else
 #endif /* CONFIG_FALLOCATE_ZERO_RANGE */
-    else if (!mode) {
+    if (!mode) {
         /* We can only fallocate at the EOF with a truncate */
         if (offset < blk_len) {
             fuse_reply_err(req, EOPNOTSUPP);
-- 
2.34.1