[PATCH 2/4] btrfs-progs: add sysfs file reading functions

Goldwyn Rodrigues
2020-08-25T15:04:09Z

Functions to read and and open sysfs files.
Given a fd, find the fsid associated with the mount and convert into
the sysfs directory to look. Read the exclusive_operation file to find
the current exclusive operation running.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
Makefile | 4 ++--
common/sysfs.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
common/utils.h | 3 +++
3 files changed, 57 insertions(+), 2 deletions(-)
create mode 100644 common/sysfs.c

diff --git a/Makefile b/Makefile
index ee57d9f8..8a267c45 100644
--- a/Makefile
+++ b/Makefile
@@ -168,8 +168,8 @@ libbtrfs_objects = send-stream.o send-utils.o kernel-lib/rbtree.o btrfs-list.o \
kernel-shared/free-space-tree.o repair.o kernel-shared/inode-item.o \
kernel-shared/file-item.o \
kernel-lib/raid56.o kernel-lib/tables.o \
- common/device-scan.o common/path-utils.o \
- common/utils.o libbtrfsutil/subvolume.o libbtrfsutil/stubs.o \
+ common/device-scan.o common/path-utils.o common/utils.o \
+ common/sysfs.o libbtrfsutil/subvolume.o libbtrfsutil/stubs.o \
crypto/hash.o crypto/xxhash.o $(CRYPTO_OBJECTS)
libbtrfs_headers = send-stream.h send-utils.h send.h kernel-lib/rbtree.h btrfs-list.h \
crypto/crc32c.h kernel-lib/list.h kerncompat.h \
diff --git a/common/sysfs.c b/common/sysfs.c
new file mode 100644
index 00000000..b2c95cfb
--- /dev/null
+++ b/common/sysfs.c
@@ -0,0 +1,52 @@
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include <unistd.h>
+#include <sys/select.h>
+#include <uuid/uuid.h>
+
+#include "common/utils.h"
+
+static char fsid_str[BTRFS_UUID_UNPARSED_SIZE] = {'\0'};
+
+int sysfs_open(int fd, const char *filename)
+{
+ u8 fsid[BTRFS_UUID_SIZE];
+ int ret;
+ char sysfs_file[128];
+
+ if (fsid_str[0] == '\0') {
+ ret = get_fsid_fd(fd, fsid);
+ if (ret < 0)
+ return ret;
+ uuid_unparse(fsid, fsid_str);
+ }
+
+ snprintf(sysfs_file, 128, "/sys/fs/btrfs/%s/%s", fsid_str, filename);
+ return open(sysfs_file, O_RDONLY);
+}
+
+int sysfs_get_str_fd(int fd, char *val, int size)
+{
+ lseek(fd, 0, SEEK_SET);
+ memset(val, '\0', size);
+ return read(fd, val, size);
+}
+
+int get_exclusive_operation(int mp_fd, char *val)
+{
+ int fd;
+ int n;
+
+ fd = sysfs_open(mp_fd, "exclusive_operation");
+ if (fd < 0)
+ return fd;
+
+ n = sysfs_get_str_fd(fd, val, BTRFS_SYSFS_EXOP_SIZE);
+ close(fd);
+
+ val[n - 1] = '\0';
+ return n;
+}
diff --git a/common/utils.h b/common/utils.h
index e34bb5a4..be8aab58 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -153,4 +153,7 @@ void init_rand_seed(u64 seed);
char *btrfs_test_for_multiple_profiles(int fd);
int btrfs_warn_multiple_profiles(int fd);

+#define BTRFS_SYSFS_EXOP_SIZE 16
+int get_exclusive_operation(int fd, char *val);
+
#endif
--
2.26.2