Re: [LTP] [PATCH 4/4] libswap: add Btrfs noCOW attribute setting for swap files

Petr Vorel
2024-01-22T08:40:21Z

Hi Li,

> The patch aims to ensure swap files on Btrfs filesystems are created
> with the appropriate FS_NOCOW_FL attribute, which is necessary to
> disable CoW (Copy-on-Write) for swap files, perthe btrfs(5) manual page.
> This change is gated behind a kernel version check to ensure compatibility
> with the system's capabilities.

> Signed-off-by: Li Wang <liwang@redhat.com>
> ---
> libs/libltpswap/libswap.c | 35 +++++++++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)

> diff --git a/libs/libltpswap/libswap.c b/libs/libltpswap/libswap.c
> index 623f2fb3c..0b1d9a227 100644
> --- a/libs/libltpswap/libswap.c
> +++ b/libs/libltpswap/libswap.c
> @@ -4,6 +4,7 @@
> * Author: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
> */

> +#include <linux/fs.h>
> #include <errno.h>

> #define TST_NO_DEFAULT_MAIN
> @@ -23,11 +24,37 @@ static const char *const swap_supported_fs[] = {
> NULL
> };

> +static void set_nocow_attr(const char *filename)
> +{
> + int fd;
> + int attrs;
> +
> + fd = SAFE_OPEN(filename, O_RDONLY);
> +
> + if (ioctl(fd, FS_IOC_GETFLAGS, &attrs) == -1) {
> + tst_res(TFAIL | TERRNO, "Error getting attributes");
I guess we don't want to break all testing due ioctl failure, right?
Otherwise I would use SAFE_IOCTL().

> + close(fd);
> + return;
> + }
> +
> + attrs |= FS_NOCOW_FL;
> +
> + if (ioctl(fd, FS_IOC_SETFLAGS, &attrs) == -1)
> + tst_res(TFAIL | TERRNO, "Error setting FS_NOCOW_FL attribute");
And here as well.

> + else
> + tst_res(TINFO, "FS_NOCOW_FL attribute set on %s\n", filename);
This is redundant new line, please remove \n before merging.

nit: make check reports various of formatting issues (on master there are only
two). Would you dare to fix them? (some of them are added in the first commit).

make check-libswap
CHECK libs/libltpswap/libswap.c
libswap.c:75: WARNING: Missing a blank line after declarations
libswap.c:101: WARNING: please, no spaces at the start of a line
libswap.c:102: WARNING: Missing a blank line after declarations
libswap.c:102: WARNING: please, no spaces at the start of a line
libswap.c:102: WARNING: suspect code indent for conditional statements (7, 15)
libswap.c:103: ERROR: code indent should use tabs where possible
libswap.c:103: WARNING: please, no spaces at the start of a line
libswap.c:103: WARNING: suspect code indent for conditional statements (15, 23)
libswap.c:104: ERROR: code indent should use tabs where possible
libswap.c:104: WARNING: please, no spaces at the start of a line
libswap.c:105: ERROR: code indent should use tabs where possible
libswap.c:105: WARNING: please, no spaces at the start of a line
libswap.c:105: WARNING: suspect code indent for conditional statements (15, 23)
libswap.c:106: ERROR: code indent should use tabs where possible
libswap.c:106: WARNING: please, no spaces at the start of a line
libswap.c:107: WARNING: please, no spaces at the start of a line

> +
> + close(fd);
> +}
> +
> /*
> * Make a swap file
> */
> int make_swapfile(const char *swapfile, int safe)
> {
> + long fs_type = tst_fs_type(swapfile);
> + const char *fstype = tst_fs_type_name(fs_type);
> +
> if (!tst_fs_has_free(".", sysconf(_SC_PAGESIZE) * 10, TST_BYTES))
> tst_brk(TBROK, "Insufficient disk space to create swap file");

> @@ -35,6 +62,14 @@ int make_swapfile(const char *swapfile, int safe)
> if (tst_fill_file(swapfile, 0, sysconf(_SC_PAGESIZE), 10) != 0)
> tst_brk(TBROK, "Failed to create swapfile");

> + /* Btrfs file need set 'nocow' attribute */
> + if (strcmp(fstype, "btrfs") == 0) {

Maybe using just fs_type (long), i.e. avoid conversion to char * via
tst_fs_type_name()? Or am I missing something?

long fs_type = tst_fs_type(swapfile);
...
if (fs_type == TST_BTRFS_MAGIC) {

Kind regards,
Petr

> + if (tst_kvercmp(5, 0, 0) > 0)
> + set_nocow_attr(swapfile);
> + else
> + tst_brk(TCONF, "Swapfile on %s not implemented", fstype);
> + }
> +
> /* make the file swapfile */
> const char *argv[2 + 1];
> argv[0] = "mkswap";