[nginx] Too large st_blocks values are now ignored (ticket #157).

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/52b34c3f89b4
branches:  
changeset: 7669:52b34c3f89b4
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon Jun 22 18:02:59 2020 +0300
description:
Too large st_blocks values are now ignored (ticket #157).

With XFS, using "allocsize=64m" mount option results in large preallocation
being reported in the st_blocks as returned by fstat() till the file is
closed.  This in turn results in incorrect cache size calculations and
wrong clearing based on max_size.

To avoid too aggressive cache clearing on such volumes, st_blocks values
which result in sizes larger than st_size and eight blocks (an arbitrary
limit) are no longer trusted, and we use st_size instead.

The ngx_de_fs_size() counterpart is intentionally not modified, as
it is used on closed files and hence not affected by this problem.

diffstat:

 src/os/unix/ngx_files.h |  5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diffs (15 lines):

diff -r 0a04e5e4c40b -r 52b34c3f89b4 src/os/unix/ngx_files.h
--- a/src/os/unix/ngx_files.h	Mon Jun 22 18:02:58 2020 +0300
+++ b/src/os/unix/ngx_files.h	Mon Jun 22 18:02:59 2020 +0300
@@ -185,7 +185,10 @@ ngx_int_t ngx_set_file_time(u_char *name
 #define ngx_is_exec(sb)          (((sb)->st_mode & S_IXUSR) == S_IXUSR)
 #define ngx_file_access(sb)      ((sb)->st_mode & 0777)
 #define ngx_file_size(sb)        (sb)->st_size
-#define ngx_file_fs_size(sb)     ngx_max((sb)->st_size, (sb)->st_blocks * 512)
+#define ngx_file_fs_size(sb)                                                 \
+    (((sb)->st_blocks * 512 > (sb)->st_size                                  \
+     && (sb)->st_blocks * 512 < (sb)->st_size + 8 * (sb)->st_blksize)        \
+     ? (sb)->st_blocks * 512 : (sb)->st_size)
 #define ngx_file_mtime(sb)       (sb)->st_mtime
 #define ngx_file_uniq(sb)        (sb)->st_ino