[musl] [PATCH] [f]statvfs: allocate spare for f_type

[musl] [PATCH] [f]statvfs: allocate spare for f_type

[наб]

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This is the only missing part in struct statvfs.
The LSB calls [f]statfs() deprecated, and its weird types are definitely
off-putting. However, its use is required to get f_type.

Instead, allocate one of the six spares to f_type,
copied directly from struct statfs.
This then becomes a small extension to the standard interface on Linux,
instead of two different interfaces, one of which is quite odd due to
being an ABI type, and there no longer is any reason to use statfs().

The underlying kernel type is a mess, but all architectures agree on u32
(or more) for the ABI, and all filesystem magicks are 32-bit integers.

Link: https://lore.kernel.org/linux-man/f54kudgblgk643u32tb6at4cd3kkzha6hslahv24szs4raroaz@ogivjbfdaqtb/t/#u
---
 include/sys/statvfs.h | 3 ++-
 src/stat/statvfs.c    | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/sys/statvfs.h b/include/sys/statvfs.h
index 57a6b806..71d9d1f9 100644
--- a/include/sys/statvfs.h
+++ b/include/sys/statvfs.h
@@ -23,7 +23,8 @@ struct statvfs {
 	unsigned long f_fsid;
 #endif
 	unsigned long f_flag, f_namemax;
-	int __reserved[6];
+	unsigned int f_type;
+	int __reserved[5];
 };
 
 int statvfs (const char *__restrict, struct statvfs *__restrict);
diff --git a/src/stat/statvfs.c b/src/stat/statvfs.c
index bfbb5fee..bc12da8b 100644
--- a/src/stat/statvfs.c
+++ b/src/stat/statvfs.c
@@ -39,6 +39,7 @@ static void fixup(struct statvfs *out, const struct statfs *in)
 	out->f_fsid = in->f_fsid.__val[0];
 	out->f_flag = in->f_flags;
 	out->f_namemax = in->f_namelen;
+	out->f_type = in->f_type;
 }
 
 int statvfs(const char *restrict path, struct statvfs *restrict buf)
-- 
2.39.2

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Re: [musl] [PATCH] [f]statvfs: allocate spare for f_type

[Szabolcs Nagy]

* наб <nabijaczleweli@nabijaczleweli.xyz> [2023-06-23 22:36:11 +0200]:
> This is the only missing part in struct statvfs.
> The LSB calls [f]statfs() deprecated, and its weird types are definitely
> off-putting. However, its use is required to get f_type.
> 
> Instead, allocate one of the six spares to f_type,
> copied directly from struct statfs.
> This then becomes a small extension to the standard interface on Linux,
> instead of two different interfaces, one of which is quite odd due to
> being an ABI type, and there no longer is any reason to use statfs().
> 
> The underlying kernel type is a mess, but all architectures agree on u32
> (or more) for the ABI, and all filesystem magicks are 32-bit integers.
> 
> Link: https://lore.kernel.org/linux-man/f54kudgblgk643u32tb6at4cd3kkzha6hslahv24szs4raroaz@ogivjbfdaqtb/t/#u

fwiw this looks good to me assuming the glibc patch gets accepted:

https://patchwork.sourceware.org/project/glibc/patch/169a6ec2a9957495275964afd0697fa3aea1c6b6.1687552604.git.nabijaczleweli@nabijaczleweli.xyz/


> ---
>  include/sys/statvfs.h | 3 ++-
>  src/stat/statvfs.c    | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sys/statvfs.h b/include/sys/statvfs.h
> index 57a6b806..71d9d1f9 100644
> --- a/include/sys/statvfs.h
> +++ b/include/sys/statvfs.h
> @@ -23,7 +23,8 @@ struct statvfs {
>  	unsigned long f_fsid;
>  #endif
>  	unsigned long f_flag, f_namemax;
> -	int __reserved[6];
> +	unsigned int f_type;
> +	int __reserved[5];
>  };
>  
>  int statvfs (const char *__restrict, struct statvfs *__restrict);
> diff --git a/src/stat/statvfs.c b/src/stat/statvfs.c
> index bfbb5fee..bc12da8b 100644
> --- a/src/stat/statvfs.c
> +++ b/src/stat/statvfs.c
> @@ -39,6 +39,7 @@ static void fixup(struct statvfs *out, const struct statfs *in)
>  	out->f_fsid = in->f_fsid.__val[0];
>  	out->f_flag = in->f_flags;
>  	out->f_namemax = in->f_namelen;
> +	out->f_type = in->f_type;
>  }
>  
>  int statvfs(const char *restrict path, struct statvfs *restrict buf)
> -- 
> 2.39.2

[musl] [PATCH v2] [f]statvfs: allocate spare for f_type

[наб]

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This is the only missing part in struct statvfs.
The LSB calls [f]statfs() deprecated, and its weird types are definitely
off-putting. However, its use is required to get f_type.

Instead, allocate one of the six spares to f_type,
copied directly from struct statfs.
This then becomes a small extension to the standard interface on Linux,
instead of two different interfaces, one of which is quite odd due to
being an ABI type, and there no longer is any reason to use statfs().

The underlying kernel type is a mess, but all architectures agree on u32
(or more) for the ABI, and all filesystem magicks are 32-bit integers.

Link: https://lore.kernel.org/linux-man/f54kudgblgk643u32tb6at4cd3kkzha6hslahv24szs4raroaz@ogivjbfdaqtb/t/#u
Link: https://sourceware.org/git/?p=glibc.git;a=commit;h=92861d93cdad13834f4d8f39504b550a80ad8200
---
Applied in glibc for 2.39, so resending rebased.

 include/sys/statvfs.h | 3 ++-
 src/stat/statvfs.c    | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/sys/statvfs.h b/include/sys/statvfs.h
index 57a6b806..71d9d1f9 100644
--- a/include/sys/statvfs.h
+++ b/include/sys/statvfs.h
@@ -23,7 +23,8 @@ struct statvfs {
 	unsigned long f_fsid;
 #endif
 	unsigned long f_flag, f_namemax;
-	int __reserved[6];
+	unsigned int f_type;
+	int __reserved[5];
 };
 
 int statvfs (const char *__restrict, struct statvfs *__restrict);
diff --git a/src/stat/statvfs.c b/src/stat/statvfs.c
index bfbb5fee..bc12da8b 100644
--- a/src/stat/statvfs.c
+++ b/src/stat/statvfs.c
@@ -39,6 +39,7 @@ static void fixup(struct statvfs *out, const struct statfs *in)
 	out->f_fsid = in->f_fsid.__val[0];
 	out->f_flag = in->f_flags;
 	out->f_namemax = in->f_namelen;
+	out->f_type = in->f_type;
 }
 
 int statvfs(const char *restrict path, struct statvfs *restrict buf)
-- 
2.39.2

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Re: [musl] [PATCH v2] [f]statvfs: allocate spare for f_type

[Rich Felker]

On Thu, Aug 17, 2023 at 10:05:14PM +0200, наб wrote:
> This is the only missing part in struct statvfs.
> The LSB calls [f]statfs() deprecated, and its weird types are definitely
> off-putting. However, its use is required to get f_type.
> 
> Instead, allocate one of the six spares to f_type,
> copied directly from struct statfs.
> This then becomes a small extension to the standard interface on Linux,
> instead of two different interfaces, one of which is quite odd due to
> being an ABI type, and there no longer is any reason to use statfs().
> 
> The underlying kernel type is a mess, but all architectures agree on u32
> (or more) for the ABI, and all filesystem magicks are 32-bit integers.

Revisiting this, the commit message was incorrect, particularly the
wording:

    "This is the only missing part in struct statvfs."

struct statvfs has unsigned long f_fsid, which is only a 32-bit field
and does not represent the full (total 64-bit) pair fsid_t from struct
statfs that Linux provides.

I did some digging into what this actually is, and on filesystems that
have a uuid in the superblock, it's a very basic hash (xor of upper
and lower half) of the uuid into a 64-bit value.

glibc combines the upper and lower half to a single 64-bit unsigned
long on 64-bit archs, but uses only the first 32-bit part on 32-bit
archs. On musl, I intentionally only used the first part to avoid a
functionality discrepancy between 32- and 64-bit archs.

Since then, gnu coreutils has switched from using statfs to statvfs,
producing a "regression" on musl and 32-bit glibc archs. Arguably this
"regression" does not matter, since the value itself is not meaningful
and there's really nothing useful you can do with it, but it's
probably worth noting.

Rich