[PATCH] btrfs-progs: mkfs: only output the warning if the sectorsize is not supported

[Qu Wenruo]

Currently mkfs.btrfs will output a warning message if the sectorsize is
not the same as page size:
  WARNING: the filesystem may not be mountable, sectorsize 4096 doesn't match 
page size 65536

But since btrfs subpage support for 64K page size is comming, this
output is populating the golden output of fstests, causing tons of false
alerts.

This patch will make teach mkfs.btrfs to check
/sys/fs/btrfs/features/supported_sectorsizes, and compare if the sector
size is supported.

Then only output above warning message if the sector size is not
supported.

Signed-off-by: Qu Wenruo <w...@suse.com>
---
 common/fsfeatures.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/common/fsfeatures.c b/common/fsfeatures.c
index 569208a9e5b1..13b775da9c72 100644
--- a/common/fsfeatures.c
+++ b/common/fsfeatures.c
@@ -16,6 +16,8 @@
 
 #include "kerncompat.h"
 #include <sys/utsname.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include <linux/version.h>
 #include <unistd.h>
 #include "common/fsfeatures.h"
@@ -327,8 +329,15 @@ u32 get_running_kernel_version(void)
 
        return version;
 }
+
+/*
+ * The buffer size if strlen("4096 8192 16384 32768 65536"),
+ * which is 28, then round up to 32.
+ */
+#define SUPPORTED_SECTORSIZE_BUF_SIZE  32
 int btrfs_check_sectorsize(u32 sectorsize)
 {
+       bool sectorsize_checked = false;
        u32 page_size = (u32)sysconf(_SC_PAGESIZE);
 
        if (!is_power_of_2(sectorsize)) {
@@ -340,7 +349,32 @@ int btrfs_check_sectorsize(u32 sectorsize)
                      sectorsize);
                return -EINVAL;
        }
-       if (page_size != sectorsize)
+       if (page_size == sectorsize) {
+               sectorsize_checked = true;
+       } else {
+               /*
+                * Check if the sector size is supported
+                */
+               char supported_buf[SUPPORTED_SECTORSIZE_BUF_SIZE] = { 0 };
+               char sectorsize_buf[SUPPORTED_SECTORSIZE_BUF_SIZE] = { 0 };
+               int fd;
+               int ret;
+
+               fd = open("/sys/fs/btrfs/features/supported_sectorsizes",
+                         O_RDONLY);
+               if (fd < 0)
+                       goto out;
+               ret = read(fd, supported_buf, sizeof(supported_buf));
+               close(fd);
+               if (ret < 0)
+                       goto out;
+               snprintf(sectorsize_buf, SUPPORTED_SECTORSIZE_BUF_SIZE,
+                        "%u", page_size);
+               if (strstr(supported_buf, sectorsize_buf))
+                       sectorsize_checked = true;
+       }
+out:
+       if (!sectorsize_checked)
                warning(
 "the filesystem may not be mountable, sectorsize %u doesn't match page size 
%u",
                        sectorsize, page_size);
-- 
2.31.1