[LTP] [PATCH] mmap21: Check for free space before mapping the file

[LTP] [PATCH] mmap21: Check for free space before mapping the file

[Victor Cheng-Yen Yang via ltp]

From: Victor Cheng-Yen Yang <cyyang772@andestech.com>

The test creates a sparse file with lseek() and a one byte write, so
mmap() allocates no blocks. The child then touches every byte and ext4
fills the holes inside ext4_page_mkwrite(). A store instruction has no
error return, so an ENOSPC there becomes VM_FAULT_SIGBUS and the test
reports only

  tst_test.c:536: TBROK: Child (13042) killed by signal SIGBUS

which says nothing about the full filesystem. The information is
available before the mapping and gone after it, so check it in setup
and report TCONF earlier as convention.

Signed-off-by: Victor Cheng-Yen Yang <cyyang772@andestech.com>
---
 testcases/kernel/syscalls/mmap/mmap21.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/testcases/kernel/syscalls/mmap/mmap21.c b/testcases/kernel/syscalls/mmap/mmap21.c
index ea3ae835a..3d6e8bd46 100644
--- a/testcases/kernel/syscalls/mmap/mmap21.c
+++ b/testcases/kernel/syscalls/mmap/mmap21.c
@@ -10,6 +10,7 @@
  * access, and read back the data from the file.
  */
 
+#include <sys/vfs.h>
 #include "tst_test.h"
 
 #define FILE_NAME "testfile"
@@ -71,11 +72,24 @@ exit:
 
 static void setup(void)
 {
+	struct statfs sf;
+	unsigned long long needed, avail;
+
 	if (tst_parse_filesize(str_pages, &pages, 1, LLONG_MAX))
 		tst_brk(TBROK, "Invalid number of pages: %s", str_pages);
 
 	memory_size = pages * getpagesize();
 
+	/* the byte written past the mapping costs a whole block */
+	SAFE_STATFS(".", &sf);
+	needed = memory_size + sf.f_bsize;
+	avail = (unsigned long long)sf.f_bavail * sf.f_bsize;
+
+	if (!tst_fs_has_free(".", needed, TST_BYTES)) {
+		tst_brk(TCONF, "Not enough free space, test needs %llu bytes, %llu available",
+			needed, avail);
+	}
+
 	buff = SAFE_MALLOC(memory_size);
 }
 
-- 
2.55.0


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Re: [LTP] mmap21: Check for free space before mapping the file

[linuxtestproject.agent]

Hi Victor,

On Tue, 8 Sep 2026, Victor Cheng-Yen Yang wrote:
> mmap21: Check for free space before mapping the file

Verdict - Reviewed

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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Re: [LTP] [PATCH] mmap21: Check for free space before mapping the file

[Cyril Hrubis]

Hi!
> The test creates a sparse file with lseek() and a one byte write, so
> mmap() allocates no blocks. The child then touches every byte and ext4
> fills the holes inside ext4_page_mkwrite(). A store instruction has no
> error return, so an ENOSPC there becomes VM_FAULT_SIGBUS and the test
> reports only
> 
>   tst_test.c:536: TBROK: Child (13042) killed by signal SIGBUS
> 
> which says nothing about the full filesystem. The information is
> available before the mapping and gone after it, so check it in setup
> and report TCONF earlier as convention.

Depending on the page size this is either 4MB or 64MB, I would say that
if you run LTP on a machine with less than 4MB of free space many tests
would fail.

Maybe it would make sense to print a warning from the test library for
any tests that has needs_tmpdir == 1 and the free space at the test
temporary directory is less than a few megabytes.

-- 
Cyril Hrubis
chrubis@suse.cz

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