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btrfs: send: make use of -fms-extensions for defining struct fs_path

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The newly introduced -fms-extensions compiler flag allows defining
struct fs_path in such a way that inline_buf becomes a proper array
with a size known to the compiler.

This also makes the problem fixed by commit 8aec9dbf2d ("btrfs: send:
fix -Wflex-array-member-not-at-end warning in struct send_ctx") go away.
Whether cur_inode_path should be put back to its original place in
struct send_ctx I don't know, but at least the comment no longer
applies.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: David Sterba <dsterba@suse.com>
Link: https://patch.msgid.link/20251020142228.1819871-3-linux@rasmusvillemoes.dk
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nicolas Schier <nsc@kernel.org>
This commit is contained in:
Rasmus Villemoes
2025-10-20 16:22:28 +02:00
committed by Nicolas Schier
parent 9716818d61
commit d599f571b3
1 changed files with 20 additions and 19 deletions
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39
fs/btrfs/send.c
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@@ -47,28 +47,30 @@
* It allows fast adding of path elements on the right side (normal path) and
* fast adding to the left side (reversed path). A reversed path can also be
* unreversed if needed.
*
* The definition of struct fs_path relies on -fms-extensions to allow
* including a tagged struct as an anonymous member.
*/
struct fs_path {
union {
struct {
char *start;
char *end;
struct __fs_path {
char *start;
char *end;
char *buf;
unsigned short buf_len:15;
unsigned short reversed:1;
char inline_buf[];
};
/*
* Average path length does not exceed 200 bytes, we'll have
* better packing in the slab and higher chance to satisfy
* an allocation later during send.
*/
char pad[256];
};
char *buf;
unsigned short buf_len:15;
unsigned short reversed:1;
};
static_assert(sizeof(struct __fs_path) < 256);
struct fs_path {
struct __fs_path;
/*
* Average path length does not exceed 200 bytes, we'll have
* better packing in the slab and higher chance to satisfy
* an allocation later during send.
*/
char inline_buf[256 - sizeof(struct __fs_path)];
};
#define FS_PATH_INLINE_SIZE \
(sizeof(struct fs_path) - offsetof(struct fs_path, inline_buf))
sizeof_field(struct fs_path, inline_buf)
/* reused for each extent */
@@ -305,7 +307,6 @@ struct send_ctx {
struct btrfs_lru_cache dir_created_cache;
struct btrfs_lru_cache dir_utimes_cache;
/* Must be last as it ends in a flexible-array member. */
struct fs_path cur_inode_path;
};