[LTP] [PATCH V3 5/5] libswap: Introduce file contiguity check

[Li Wang]

This patch introduces a new function file_is_contiguous to the
libltpswap library to determine if a swap file is stored in a
contiguous block of disk space, which is a typical requirement
for swap files in Linux. The function performs a series of checks
using the fiemap structure to assess the contiguity of the file
and logs the result.

It is integrated into the is_swap_supported function to replace
the previous tst_fibmap check, providing a more reliable method
for verifying that a file suitable for swap is indeed contiguous.

Signed-off-by: Li Wang <liwang@redhat.com>
---
 libs/libltpswap/libswap.c | 72 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 67 insertions(+), 5 deletions(-)

diff --git a/libs/libltpswap/libswap.c b/libs/libltpswap/libswap.c
index b253dbeec..8382ea23c 100644
--- a/libs/libltpswap/libswap.c
+++ b/libs/libltpswap/libswap.c
@@ -6,6 +6,8 @@
 
 #include <linux/fs.h>
 #include <errno.h>
+#include <linux/fiemap.h>
+#include <stdlib.h>
 
 #define TST_NO_DEFAULT_MAIN
 
@@ -69,6 +71,63 @@ static int prealloc_contiguous_file(const char *path, size_t bs, size_t bcount)
 	return 0;
 }
 
+static int file_is_contiguous(const char *filename)
+{
+	int fd, contiguous = 0;
+	struct fiemap *fiemap;
+
+	if (tst_fibmap(filename) == 0) {
+		contiguous = 1;
+		goto out;
+	}
+
+	if (tst_fs_type(filename) == TST_TMPFS_MAGIC) {
+		contiguous = 0;
+		goto out;
+	}
+
+	fd = SAFE_OPEN(filename, O_RDONLY);
+
+	fiemap = (struct fiemap *)SAFE_MALLOC(sizeof(struct fiemap) + sizeof(struct fiemap_extent));
+	memset(fiemap, 0, sizeof(struct fiemap) + sizeof(struct fiemap_extent));
+
+	fiemap->fm_start = 0;
+	fiemap->fm_length = ~0;
+	fiemap->fm_flags = 0;
+	fiemap->fm_extent_count = 1;
+
+	SAFE_IOCTL(fd, FS_IOC_FIEMAP, fiemap);
+
+	/*
+	 * fiemap->fm_mapped_extents != 1:
+	 *   This checks if the file does not have exactly one extent. If there are more
+	 *   or zero extents, the file is not stored in a single contiguous block.
+	 *
+	 * fiemap->fm_extents[0].fe_logical != 0:
+	 *   This checks if the first extent does not start at the logical offset 0 of
+	 *   the file. If it doesn't, it indicates that the file's first block of data
+	 *   is not at the beginning of the file, which implies non-contiguity.
+	 *
+	 * (fiemap->fm_extents[0].fe_flags & FIEMAP_EXTENT_LAST) != FIEMAP_EXTENT_LAST:
+	 *   This checks if the first extent does not have the FIEMAP_EXTENT_LAST flag set.
+	 *   If the flag isn't set, it means that this extent is not the last one, suggesting
+	 *   that there are more extents and the file is not contiguous.
+	 */
+	if (fiemap->fm_mapped_extents != 1 ||
+		fiemap->fm_extents[0].fe_logical != 0 ||
+		(fiemap->fm_extents[0].fe_flags & FIEMAP_EXTENT_LAST) != FIEMAP_EXTENT_LAST) {
+
+		tst_res(TINFO, "File '%s' is not contiguous", filename);
+		contiguous = 0;
+	}
+
+	SAFE_CLOSE(fd);
+	free(fiemap);
+
+out:
+	return contiguous;
+}
+
 /*
  * Make a swap file
  */
@@ -99,10 +158,15 @@ int make_swapfile(const char *swapfile, int safe)
 void is_swap_supported(const char *filename)
 {
 	int i, sw_support = 0;
-	int fibmap = tst_fibmap(filename);
+	int ret = make_swapfile(filename, 1);
+	int fi_contiguous = file_is_contiguous(filename);
 	long fs_type = tst_fs_type(filename);
 	const char *fstype = tst_fs_type_name(fs_type);
 
+	if (fs_type == TST_BTRFS_MAGIC &&
+			tst_kvercmp(5, 0, 0) < 0)
+		tst_brk(TCONF, "Swapfile on Btrfs (kernel < 5.0) not implemented");
+
 	for (i = 0; swap_supported_fs[i]; i++) {
 		if (strstr(fstype, swap_supported_fs[i])) {
 			sw_support = 1;
@@ -110,10 +174,8 @@ void is_swap_supported(const char *filename)
 		}
 	}
 
-	int ret = make_swapfile(filename, 1);
-
 	if (ret != 0) {
-		if (fibmap == 1 && sw_support == 0)
+		if (fi_contiguous == 0 && sw_support == 0)
 			tst_brk(TCONF, "mkswap on %s not supported", fstype);
 		else
 			tst_brk(TFAIL, "mkswap on %s failed", fstype);
@@ -123,7 +185,7 @@ void is_swap_supported(const char *filename)
 	if (TST_RET == -1) {
 		if (errno == EPERM)
 			tst_brk(TCONF, "Permission denied for swapon()");
-		else if (fibmap == 1 && errno == EINVAL && sw_support == 0)
+		else if (errno == EINVAL && fi_contiguous == 0 && sw_support == 0)
 			tst_brk(TCONF, "Swapfile on %s not implemented", fstype);
 		else
 			tst_brk(TFAIL | TTERRNO, "swapon() on %s failed", fstype);
-- 
2.40.1