Sorry, I forgot to reply...
On 2025-02-21 20:33:21 +0100, Salvatore Bonaccorso wrote:
> Let's start from:
>
> https://www.kernel.org/doc/html/latest/filesystems/vfs.html#mount-options
>
> The important bits are:
>
> Showing options
> ---------------
>
> If a filesystem accepts mount options, it must define show_options() to
> show all the currently active options. The rules are:
>
> - options MUST be shown which are not default or their values differ
> from the default
>
> - options MAY be shown which are enabled by default or have their
> default value
But, IMHO, a fixed choice should be made. This should not be random.
Otherwise, this is confusing, and can break scripts that detect
changes in the configuration.
Now, with your analysis of the code...
> tmpfs is defined in "mm/shmem.c and we have (current mainline):
>
> 5263 #ifdef CONFIG_TMPFS
> 5264 .statfs = shmem_statfs,
> 5265 .show_options = shmem_show_options,
> 5266 #endif
>
> shmem_show_options() handles showming mount options for tmpfs:
>
> 4878 static int shmem_show_options(struct seq_file *seq, struct dentry *root)
> 4879 {
> 4880 struct shmem_sb_info *sbinfo = SHMEM_SB(root->d_sb);
> 4881 struct mempolicy *mpol;
> 4882
> 4883 if (sbinfo->max_blocks != shmem_default_max_blocks())
> 4884 seq_printf(seq, ",size=%luk", K(sbinfo->max_blocks));
> [...]
>
> So size is only showed if sbinfo->max_blocks != shmem_default_max_blocks().
>
> Let's look at shmem_default_max_blocks():
>
> 147 #ifdef CONFIG_TMPFS
> 148 static unsigned long shmem_default_max_blocks(void)
> 149 {
> 150 return totalram_pages() / 2;
> 151 }
>
> So this is 50% of ram as *default* which matches tmpfs(5):
>
> Mount options
> The tmpfs filesystem supports the following mount options:
>
> size=bytes
> 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 0.
>
> The size may have a k, m, or g suffix for Ki, Mi, Gi (bi‐
> nary kilo (kibi), binary mega (mebi), and binary giga
> (gibi)).
>
> The size may also have a % suffix to limit this instance
> to a percentage of physical RAM.
>
> The default, when neither size nor nr_blocks is speci‐
> fied, is size=50%.
>
> So my undestanding would be that the code here is coherent with the
> specification that if size corresponds to the default value, the code
> may, but does not must show it.
>
> Does this make sense?
According to the above code, the size is never shown for the default
as the condition sbinfo->max_blocks != shmem_default_max_blocks() is
false. But this is not what I observe: the size is shown randomly
(more precisely, whether the size is shown is chosen at boot time),
though it is always the default here.
--
Vincent Lefèvre <vinc...@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)
