The libxcmd code builds up a table that records information about
all filesystems that might be subject to quotas, as well as a set
of directories that are the roots of project quota trees.
When building the table, the device number for each affected
filesystem is determined (in fs_device_number()) using a call to
stat64(). It turns out that in all cases when doing this, a
directory path (and *not* a device special file path) is specified,
in which case the appropriate filesystem device id is found in the
st_dev field produce by the call to stat64() (i.e., the device id
for the mounted filesystem containing the path). Accordingly,
fs_device_number() always returns the st_dev field.
Another routine, fs_table_lookup(), looks up an entry in this table
based on the path name provided. However this function allows a
path to a device special file be provided. In that case the right
device id to use is found in the st_rdev field returned by stat64().
I found this to be confusing, and it took a while to convince
myself that this wasn't actually bug. (It wasn't initially clear
that device special files were never passed to fs_device_number().)
In order to prevent myself and others from ever wasting time like
this again, use fs_device_number() every time a device number is
needed, and in doing so determine it consistently in all cases (that
is--use st_rdev for device special files and st_dev otherwise).
In the process, change fs_device_number() to return an zero on
success (or an errno) rather than its first argument (or NULL).
Signed-off-by: Alex Elder <aelder@xxxxxxx>
---
libxcmd/paths.c | 46 +++++++++++++++++++++-------------------------
1 files changed, 21 insertions(+), 25 deletions(-)
diff --git a/libxcmd/paths.c b/libxcmd/paths.c
index aa0aeb6..f4110d4 100644
--- a/libxcmd/paths.c
+++ b/libxcmd/paths.c
@@ -37,18 +37,26 @@ struct fs_path *fs_path;
char *mtab_file;
#define PROC_MOUNTS "/proc/self/mounts"
-static char *
+static int
fs_device_number(
- char *name,
+ const char *name,
dev_t *devnum)
{
struct stat64 sbuf;
if (stat64(name, &sbuf) < 0)
- return NULL;
- *devnum = sbuf.st_dev;
+ return errno;
+ /*
+ * We want to match st_rdev if the path provided is a device
+ * special file. Otherwise we are looking for the the
+ * device id for the containing filesystem, in st_dev.
+ */
+ if (S_ISBLK(sbuf.st_mode) || S_ISCHR(sbuf.st_mode))
+ *devnum = sbuf.st_rdev;
+ else
+ *devnum = sbuf.st_dev;
- return name;
+ return 0;
}
/*
@@ -61,23 +69,12 @@ fs_table_lookup(
const char *dir,
uint flags)
{
- struct stat64 sbuf;
uint i;
- dev_t dev;
+ dev_t dev = 0;
- if (stat64(dir, &sbuf) < 0)
+ if (fs_device_number(dir, &dev))
return NULL;
- /*
- * We want to match st_rdev if the directory provided is a
- * device special file. Otherwise we are looking for the
- * the device id for the containing filesystem, in st_dev.
- */
- if (S_ISBLK(sbuf.st_mode) || S_ISCHR(sbuf.st_mode))
- dev = sbuf.st_rdev;
- else
- dev = sbuf.st_dev;
-
for (i = 0; i < fs_count; i++) {
if ((flags & fs_table[i].fs_flags) == 0)
continue;
@@ -103,11 +100,11 @@ fs_table_insert(
return EINVAL;
datadev = logdev = rtdev = 0;
- if (!fs_device_number(dir, &datadev))
+ if (fs_device_number(dir, &datadev))
return errno;
- if (fslog && !fs_device_number(fslog, &logdev))
+ if (fslog && fs_device_number(fslog, &logdev))
return errno;
- if (fsrt && !fs_device_number(fsrt, &rtdev))
+ if (fsrt && fs_device_number(fsrt, &rtdev))
return errno;
tmp_fs_table = realloc(fs_table, sizeof(fs_path_t) * (fs_count + 1));
@@ -293,15 +290,14 @@ fs_mount_point_from_path(
{
fs_cursor_t cursor;
fs_path_t *fs;
- struct stat64 s;
+ dev_t dev = 0;
- if (stat64(dir, &s) < 0) {
+ if (fs_device_number(dir, &dev))
return NULL;
- }
fs_cursor_initialise(NULL, FS_MOUNT_POINT, &cursor);
while ((fs = fs_cursor_next_entry(&cursor))) {
- if (fs->fs_datadev == s.st_dev)
+ if (fs->fs_datadev == dev)
break;
}
return fs;
--
1.7.6.2
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