tmpfs.5: Document that size/blocks=0 and nr_inodes=0 remove the limits

Bitten by this again.  Behaviour blames back to at least 2005
(probably original to shmem.c), documented upstream in
Documentation/filesystems/tmpfs.rst (formerly .txt).

For example:

  # mount -t tmpfs -o size=0 tmpfs /etc/
  # df /etc/
  Filesystem 1k-blocks Used Avail Use% Mounted on
  tmpfs              0    0     0    - /etc
  # head -c100M  < /dev/urandom > /etc/passwd
  # df /etc/
  Filesystem 1k-blocks Used Avail Use% Mounted on
  tmpfs              0    0     0    - /etc
  # ls -l /etc/passwd
  -rw-r--r-- 1 0 0 104857600 08-12 19:55 /etc/passwd
  # du /etc/passwd
  204800  /etc/passwd

whereas the current manual insinuates head should ENOSPC instantly.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Cc: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

diff --git a/man5/tmpfs.5 b/man5/tmpfs.5
index cdd5f2fd8698922d2fb90e4c374ec7a869a4197a..5274e632d6fdd35c37b99e108c60292ba6638012 100644 (file)
--- a/man5/tmpfs.5
+++ b/man5/tmpfs.5
@@ -51,6 +51,8 @@ filesystem supports the following mount options:
 .BR size "=\fIbytes\fP"
 Specify an upper limit on the size of the filesystem.
 The size is given in bytes, and rounded up to entire pages.
+The limit is removed if the size is
+.BR 0 .
 .IP
 The size may have a
 .BR k ,
@@ -89,6 +91,8 @@ but not a % suffix.
 The maximum number of inodes for this instance.
 The default is half of the number of your physical RAM pages, or (on a
 machine with highmem) the number of lowmem RAM pages, whichever is smaller.
+The limit is removed if the number is
+.BR 0 .
 .IP
 Inodes may be specified with
 .BR k ,