[nginx] Large block sizes on Linux are now ignored (ticket #1168).

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/0a04e5e4c40b
branches:  
changeset: 7668:0a04e5e4c40b
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon Jun 22 18:02:58 2020 +0300
description:
Large block sizes on Linux are now ignored (ticket #1168).

NFS on Linux is known to report wsize as a block size (in both f_bsize
and f_frsize, both in statfs() and statvfs()).  On the other hand,
typical file system block sizes on Linux (ext2/ext3/ext4, XFS) are limited
to pagesize.  (With FAT, block sizes can be at least up to 512k in
extreme cases, but this doesn't really matter, see below.)
To avoid too aggressive cache clearing on NFS volumes on Linux, block
sizes larger than pagesize are now ignored.

Note that it is safe to ignore large block sizes.  Since 3899:e7cd13b7f759
(1.0.1) cache size is calculated based on fstat() st_blocks, and rounding
to file system block size is preserved mostly for Windows.

Note well that on other OSes valid block sizes seen are at least up
to 65536.  In particular, UFS on FreeBSD is known to work well with block
and fragment sizes set to 65536.

diffstat:

 src/os/unix/ngx_files.c |  12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diffs (29 lines):

diff -r 1ece2ac2555a -r 0a04e5e4c40b src/os/unix/ngx_files.c
--- a/src/os/unix/ngx_files.c	Mon Jun 15 20:17:16 2020 +0300
+++ b/src/os/unix/ngx_files.c	Mon Jun 22 18:02:58 2020 +0300
@@ -875,6 +875,12 @@ ngx_fs_bsize(u_char *name)
         return 512;
     }
 
+#if (NGX_LINUX)
+    if ((size_t) fs.f_bsize > ngx_pagesize) {
+        return 512;
+    }
+#endif
+
     return (size_t) fs.f_bsize;
 }
 
@@ -893,6 +899,12 @@ ngx_fs_bsize(u_char *name)
         return 512;
     }
 
+#if (NGX_LINUX)
+    if ((size_t) fs.f_frsize > ngx_pagesize) {
+        return 512;
+    }
+#endif
+
     return (size_t) fs.f_frsize;
 }