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Subject[PATCH] mm: swapfile: fix /proc/swaps heading and Size/Used/Priority alignment
Date
From: Randy Dunlap <rdunlap@infradead.org>

Fix the heading and Size/Used/Priority field alignments in
/proc/swaps. If the Size and/or Used value is >= 10000000 (8 bytes),
then the alignment by using tab characters is broken.

This patch maintains the use of tabs for alignment. If spaces
are preferred, we can just use a Field Width specifier for the
bytes and inuse fields. That way those fields don't have to be
a multiple of 8 bytes in width. E.g., with a field width of 12,
both Size and Used would always fit on the first line of an
80-column wide terminal (only Priority would be on the second line).

There are actually 2 problems: heading alignment and field width.
On an xterm, if Used is 7 bytes in length, the tab does nothing, and
the display is like this, with no space/tab between the Used and
Priority fields. (ugh)

Filename Type Size Used Priority
/dev/sda8 partition 16779260 2023012-1

To be clear, if one does 'cat /proc/swaps >/tmp/proc.swaps', it does
look different, like so:

Filename Type Size Used Priority
/dev/sda8 partition 16779260 2086988 -1

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
mm/swapfile.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- linux-next-20200521.orig/mm/swapfile.c
+++ linux-next-20200521/mm/swapfile.c
@@ -2753,20 +2753,24 @@ static int swap_show(struct seq_file *sw
struct swap_info_struct *si = v;
struct file *file;
int len;
+ unsigned int bytes, inuse;

if (si == SEQ_START_TOKEN) {
- seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
+ seq_puts(swap,"Filename\t\t\t\tType\t\tSize\t\tUsed\t\tPriority\n");
return 0;
}

+ bytes = si->pages << (PAGE_SHIFT - 10);
+ inuse = si->inuse_pages << (PAGE_SHIFT - 10);
+
file = si->swap_file;
len = seq_file_path(swap, file, " \t\n\\");
- seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
+ seq_printf(swap, "%*s%s\t%u\t%s%u\t%s%d\n",
len < 40 ? 40 - len : 1, " ",
S_ISBLK(file_inode(file)->i_mode) ?
"partition" : "file\t",
- si->pages << (PAGE_SHIFT - 10),
- si->inuse_pages << (PAGE_SHIFT - 10),
+ bytes, bytes < 10000000 ? "\t" : "",
+ inuse, inuse < 10000000 ? "\t" : "",
si->prio);
return 0;
}

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