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df vs. long-named /dev/disk/by-uuid/... file system device names
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From: |
Jim Meyering |
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Subject: |
df vs. long-named /dev/disk/by-uuid/... file system device names |
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Date: |
Thu, 29 Dec 2011 15:09:03 +0100 |
On systems with recent kernel/tools, a symlink from /etc/mtab to
/proc/mounts, and a by-UUID mount (i.e., soon, nearly everyone),
you will see something like the following when running "df -hT":
Filesystem Type Size Used
Avail Use% Mounted on
rootfs rootfs 11G 1.9G
8.0G 19% /
udev devtmpfs 3.8G 0
3.8G 0% /dev
tmpfs tmpfs 774M 376K
774M 1% /run
/dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7096a2edb66 ext4 11G 1.9G
8.0G 19% /
tmpfs tmpfs 1.6G 8.0K
1.6G 1% /run/shm
/dev/sda2 ext3 494M 78M
392M 17% /boot
/dev/sda5 ext4 12G 7.6G
3.7G 68% /usr
/dev/sda6 ext4 9.9G 6.6G
2.8G 71% /var
Contrast that with what we're used to seeing (modulo the
two entries mounted on "/", which is a separate problem):
Filesystem Type Size Used Avail Use% Mounted on
rootfs rootfs 11G 1.9G 8.0G 19% /
udev devtmpfs 3.8G 0 3.8G 0% /dev
tmpfs tmpfs 774M 376K 774M 1% /run
/dev/sda3 ext4 11G 1.9G 8.0G 19% /
tmpfs tmpfs 1.6G 8.0K 1.6G 1% /run/shm
/dev/sda2 ext3 494M 78M 392M 17% /boot
/dev/sda5 ext4 12G 7.6G 3.7G 68% /usr
/dev/sda6 ext4 9.9G 6.6G 2.8G 71% /var
When that long /dev/disk/by-*/... name is merely a symlink
to a much shorter (and often more useful) device name like
"/dev/sda3", and when it's part of a listing of all file systems,
I would much prefer to see only the latter.
I.e., if I explicitly run
"df -hT /dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7096a2edb66",
*then*, it's fine -- and expected -- to print to the long name.
It was explicitly given. However, with no non-option argument,
df should print the shorter name. Note that performing this
translation at a lower level (via a change to gnulib's mountlist.c)
would make it impossible to distinguish those two cases.
Here's a patch to do that.
It's a little larger than you might expect because of two factors:
- it modifies each of five get_dev call-points
- to avoid introducing a leak, it allocates space for dev_name earlier
I hesitated to make this change, because it feels like a kludge that's
working around a misfeature that should be fixed elsewhere. I'd rather
that the long root device name not appear in the mount listing
(/proc/mounts) in the first place.
If anyone can assure us that this will soon be "fixed" so that we
don't get such entries in /proc/mounts quite so easily, I'll be
happy to defer or drop the patch.
>From a59338b9ca2ed8cbc82bdf3a299c4a664ad113c9 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Thu, 29 Dec 2011 14:49:00 +0100
Subject: [PATCH] df: work around long-named /dev/disk/by-uuid/... symlinks
On systems with recent kernel/tools, a symlink from /etc/mtab to
/proc/mounts, and a by-UUID mount (i.e., soon, nearly everyone),
you will see something like the following when running "df -hT":
(this has been truncated to fit in a width-limited ChangeLog file)
Filesystem Type Siz...
rootfs rootfs 11G
udev devtmpfs 3.8G
tmpfs tmpfs 774M
/dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7096a2edb66 ext4 11G
tmpfs tmpfs 1.6G
/dev/sda2 ext3 494M
/dev/sda5 ext4 12G
/dev/sda6 ext4 9.9G
Contrast that with what we're used to seeing (modulo the
two entries mounted on "/", which is a separate problem):
Filesystem Type Size Used Avail Use% Mounted on
rootfs rootfs 11G 1.9G 8.0G 19% /
udev devtmpfs 3.8G 0 3.8G 0% /dev
tmpfs tmpfs 774M 376K 774M 1% /run
/dev/sda3 ext4 11G 1.9G 8.0G 19% /
tmpfs tmpfs 1.6G 8.0K 1.6G 1% /run/shm
/dev/sda2 ext3 494M 78M 392M 17% /boot
/dev/sda5 ext4 12G 7.6G 3.7G 68% /usr
/dev/sda6 ext4 9.9G 6.6G 2.8G 71% /var
When that long /dev/disk/by-*/... name is merely a symlink
to a much shorter (and often more useful) device name like
"/dev/sda3", and when it's part of a listing of all file systems,
I would much prefer to see only the latter.
I.e., if I explicitly run
"df -hT /dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7096a2edb66",
Then, it's fine -- and expected -- to print to the long name.
It was explicitly given. However, with no non-option argument,
df should print the shorter name. Note that performing this
translation at a lower level (via a change to gnulib's mountlist.c)
would make it impossible to distinguish those two cases.
* src/df.c: Include "canonicalize.h".
(get_dev): Add a parameter, telling when to resolve device symlinks
and update all callers. When true, resolve a symlink name to a
shorter referent.
Reported by Dan Jacobson in http://bugs.gnu.org/10363
---
src/df.c | 43 +++++++++++++++++++++++++++++++++++--------
1 files changed, 35 insertions(+), 8 deletions(-)
diff --git a/src/df.c b/src/df.c
index 982d607..516288b 100644
--- a/src/df.c
+++ b/src/df.c
@@ -25,6 +25,7 @@
#include <assert.h>
#include "system.h"
+#include "canonicalize.h"
#include "error.h"
#include "fsusage.h"
#include "human.h"
@@ -428,13 +429,16 @@ add_uint_with_neg_flag (uintmax_t *dest, bool *dest_neg,
If FSTYPE is non-NULL, it is the type of the file system on DISK.
If MOUNT_POINT is non-NULL, then DISK may be NULL -- certain systems may
not be able to produce statistics in this case.
- ME_DUMMY and ME_REMOTE are the mount entry flags. */
+ ME_DUMMY and ME_REMOTE are the mount entry flags.
+ RESOLVE_DEVICE_SYMLINK is true when iterating over all entries, as when
+ df is invoked with no non-option argument. See below for details. */
static void
get_dev (char const *disk, char const *mount_point,
char const *stat_file, char const *fstype,
bool me_dummy, bool me_remote,
- const struct fs_usage *force_fsu)
+ const struct fs_usage *force_fsu,
+ bool resolve_device_symlink)
{
struct fs_usage fsu;
char buf[LONGEST_HUMAN_READABLE + 2];
@@ -488,6 +492,29 @@ get_dev (char const *disk, char const *mount_point,
if (! disk)
disk = "-"; /* unknown */
+
+ char *dev_name = xstrdup (disk);
+ char *resolved_dev;
+ size_t orig_len = strlen (dev_name);
+
+ /* If dev_name is a long-named symlink like
+ /dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7196a2edb66 and its
+ canonical name is shorter, use the shorter name. But don't bother
+ checking when DEV_NAME is no longer than e.g., "/dev/sda1" */
+ if (resolve_device_symlink && 9 < orig_len
+ && (resolved_dev = canonicalize_filename_mode (dev_name, CAN_EXISTING)))
+ {
+ if (strlen (resolved_dev) < orig_len)
+ {
+ free (dev_name);
+ dev_name = resolved_dev;
+ }
+ else
+ {
+ free (resolved_dev);
+ }
+ }
+
if (! fstype)
fstype = "-"; /* unknown */
@@ -537,7 +564,7 @@ get_dev (char const *disk, char const *mount_point,
switch (field)
{
case DEV_FIELD:
- cell = xstrdup (disk);
+ cell = dev_name;
break;
case TYPE_FIELD:
@@ -648,7 +675,7 @@ get_disk (char const *disk)
{
get_dev (best_match->me_devname, best_match->me_mountdir, NULL,
best_match->me_type, best_match->me_dummy,
- best_match->me_remote, NULL);
+ best_match->me_remote, NULL, false);
return true;
}
@@ -734,7 +761,7 @@ get_point (const char *point, const struct stat *statp)
if (best_match)
get_dev (best_match->me_devname, best_match->me_mountdir, point,
best_match->me_type, best_match->me_dummy, best_match->me_remote,
- NULL);
+ NULL, false);
else
{
/* We couldn't find the mount entry corresponding to POINT. Go ahead and
@@ -745,7 +772,7 @@ get_point (const char *point, const struct stat *statp)
char *mp = find_mount_point (point, statp);
if (mp)
{
- get_dev (NULL, mp, NULL, NULL, false, false, NULL);
+ get_dev (NULL, mp, NULL, NULL, false, false, NULL, false);
free (mp);
}
}
@@ -774,7 +801,7 @@ get_all_entries (void)
for (me = mount_list; me; me = me->me_next)
get_dev (me->me_devname, me->me_mountdir, NULL, me->me_type,
- me->me_dummy, me->me_remote, NULL);
+ me->me_dummy, me->me_remote, NULL, true);
}
/* Add FSTYPE to the list of file system types to display. */
@@ -1066,7 +1093,7 @@ main (int argc, char **argv)
{
if (inode_format)
grand_fsu.fsu_blocks = 1;
- get_dev ("total", NULL, NULL, NULL, false, false, &grand_fsu);
+ get_dev ("total", NULL, NULL, NULL, false, false, &grand_fsu, false);
}
print_table ();
--
1.7.7.3
- df vs. long-named /dev/disk/by-uuid/... file system device names,
Jim Meyering <=