Re: [LTP] [PATCH 2/3] swapon03: Try to swapon() as many files until it fails

[Avinesh Kumar <akumar@suse.de>]

Hi Petr,
some comments inline

On Wednesday, November 5, 2025 4:47:15 PM CET Petr Vorel wrote:
> Previously tst_max_swapfiles() had fine tuning for a specific kernel
> version which was fragile due various backports in enterprise kernels.
> 
> Let's try to create and use as many swap files until swapon() fails.
> Then check for expected EPERM.
> 
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Petr Vorel <pvorel@suse.cz>
> ---
>  testcases/kernel/syscalls/swapon/swapon03.c | 63 +++++++++++++--------
>  1 file changed, 40 insertions(+), 23 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/swapon/swapon03.c b/testcases/kernel/syscalls/swapon/swapon03.c
> index b89d853188..0027f874be 100644
> --- a/testcases/kernel/syscalls/swapon/swapon03.c
> +++ b/testcases/kernel/syscalls/swapon/swapon03.c
> @@ -1,14 +1,18 @@
>  // SPDX-License-Identifier: GPL-2.0-or-later
>  /*
> + * Copyright (c) Linux Test Project, 2009-2025
>   * Copyright (c) International Business Machines Corp., 2007
>   * Created by <rsalveti@linux.vnet.ibm.com>
> - *
>   */
>  
>  /*\
> - * This test case checks whether swapon(2) system call returns:
> + * Test checks whether :man2:`swapon` system call returns EPERM when the maximum
> + * number of swap files are already in use.
>   *
> - *  - EPERM when there are more than MAX_SWAPFILES already in use.
> + * NOTE: test does not try to calculate MAX_SWAPFILES from the internal
> + * kernel implementation (which is currently <23, 29> depending on kernel
> + * configuration). Instead test exptect that at least 15 swap files minus
> + * currently used swap can be created.
>   */
>  
>  #include <stdio.h>
> @@ -20,49 +24,54 @@
>  #include "lapi/syscalls.h"
>  #include "libswap.h"
>  
> +#define NUM_SWAP_FILES 15
>  #define MNTPOINT	"mntpoint"
>  #define TEST_FILE	MNTPOINT"/testswap"
>  
> -static int swapfiles;
> +static int *swapfiles;
>  
>  static void setup_swap(void)
>  {
>  	pid_t pid;
> -	int status;
> -	int j, max_swapfiles, used_swapfiles;
> +	int status, used_swapfiles, expected_swapfiles;
>  	char filename[FILENAME_MAX];
>  
>  	SAFE_SETEUID(0);
>  
> -	/* Determine how many more files are to be created */
> -	max_swapfiles = tst_max_swapfiles();
>  	used_swapfiles = tst_count_swaps();
> -	swapfiles = max_swapfiles - used_swapfiles;
> -	if (swapfiles > max_swapfiles)
> -		swapfiles = max_swapfiles;
> +	expected_swapfiles = NUM_SWAP_FILES - used_swapfiles;
> +
> +	if (expected_swapfiles < 0) {
do we want to proceed when expected_swapfiles is 0 here?
> +		tst_brk(TCONF, "Warning: too many used swap files (%d)",
> +			expected_swapfiles);
I think this should be used_swapfiles ?
> +	}
>  
>  	pid = SAFE_FORK();
>  	if (pid == 0) {
> -		/*create and turn on remaining swapfiles */
> -		for (j = 0; j < swapfiles; j++) {
> -
> +		while (true) {
>  			/* Create the swapfile */
> -			snprintf(filename, sizeof(filename), "%s%02d", TEST_FILE, j + 2);
> +			snprintf(filename, sizeof(filename), "%s%02d", TEST_FILE, *swapfiles);
>  			MAKE_SMALL_SWAPFILE(filename);
>  
> -			/* turn on the swap file */
> -			TST_EXP_PASS_SILENT(swapon(filename, 0));
> +			/* Quit on a first swap file over max */
> +			if (swapon(filename, 0) == -1)
so now first swapon() fail is here and then we check for errno==EPERM by
making another swapon() call in verify_swapon function.
Is it possible to combine setup_swap() and verify_swapon() and check for
EPERM on first swapon() fail itself?

> +				break;
> +			(*swapfiles)++;
>  		}
>  		exit(0);
>  	} else {
>  		waitpid(pid, &status, 0);
>  	}
>  
> -	if (WEXITSTATUS(status))
> +	if (WEXITSTATUS(status) || *swapfiles == 0)
>  		tst_brk(TBROK, "Failed to setup swap files");
>  
> -	tst_res(TINFO, "Successfully created %d swap files", swapfiles);
> -	MAKE_SMALL_SWAPFILE(TEST_FILE);
> +	if (*swapfiles < expected_swapfiles) {
> +		tst_res(TWARN, "Successfully created only %d swap files (>= %d expected)",
> +			*swapfiles, expected_swapfiles);
> +	} else {
> +		tst_res(TINFO, "Successfully created %d swap files", *swapfiles);
> +	}
>  }
>  
>  /*
> @@ -86,8 +95,8 @@ static void clean_swap(void)
>  	int j;
>  	char filename[FILENAME_MAX];
>  
> -	for (j = 0; j < swapfiles; j++) {
> -		snprintf(filename, sizeof(filename), "%s%02d", TEST_FILE, j + 2);
> +	for (j = 0; j < *swapfiles; j++) {
> +		snprintf(filename, sizeof(filename), "%s%02d", TEST_FILE, j);
>  		check_and_swapoff(filename);
>  	}
>  
> @@ -105,12 +114,20 @@ static void setup(void)
>  		tst_brk(TCONF, "swap not supported by kernel");
>  
>  	is_swap_supported(TEST_FILE);
> +
> +	swapfiles = SAFE_MMAP(NULL, sizeof(*swapfiles), PROT_READ | PROT_WRITE,
> +			MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> +	*swapfiles = 0;
> +
>  	setup_swap();
>  }
>  
>  static void cleanup(void)
>  {
> -	clean_swap();
> +	if (swapfiles) {
> +		clean_swap();
> +		SAFE_MUNMAP(swapfiles, sizeof(*swapfiles));
> +	}
>  }
>  
>  static struct tst_test test = {
> 

Regards,
Avinesh



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