Re: [PATCH v9 08/10] open: openat2(2) syscall
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Date: 2019-07-18 14:48:22
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linux-alpha, linux-api, linux-arch, linux-arm-kernel, linux-fsdevel, linux-kselftest, linux-mips, linux-s390, linux-sh, lkml, sparclinux
On 06/07/2019 16.57, Aleksa Sarai wrote:
quoted hunk ↗ jump to hunk
--- a/fs/open.c +++ b/fs/open.c@@ -928,24 +928,32 @@ struct file *open_with_fake_path(const struct path *path, int flags, } EXPORT_SYMBOL(open_with_fake_path); -static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op) +static inline int build_open_flags(struct open_how how, struct open_flags *op) {
How does passing such a huge struct by value affect code generation? Does gcc actually inline the function (and does it even inline the old one given that it's already non-trivial and has more than one caller).
int lookup_flags = 0; - int acc_mode = ACC_MODE(flags); + int opath_mask = 0; + int acc_mode = ACC_MODE(how.flags); + + if (how.resolve & ~VALID_RESOLVE_FLAGS) + return -EINVAL; + if (!(how.flags & (O_PATH | O_CREAT | __O_TMPFILE)) && how.mode != 0) + return -EINVAL; + if (memchr_inv(how.reserved, 0, sizeof(how.reserved))) + return -EINVAL;
How about passing how by const reference, and copy the few fields you need to local variables. That would at least simplify this patch by eliminating a lot of the
- flags &= VALID_OPEN_FLAGS; + how.flags &= VALID_OPEN_FLAGS; - if (flags & (O_CREAT | __O_TMPFILE)) - op->mode = (mode & S_IALLUGO) | S_IFREG; + if (how.flags & (O_CREAT | __O_TMPFILE)) + op->mode = (how.mode & S_IALLUGO) | S_IFREG;
churn.
quoted hunk ↗ jump to hunk
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index 2868ae6c8fc1..e59917292213 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h@@ -4,13 +4,26 @@ #include <uapi/linux/fcntl.h> -/* list of all valid flags for the open/openat flags argument: */ +/* Should open_how.mode be set for older syscalls wrappers? */ +#define OPENHOW_MODE(flags, mode) \ + (((flags) | (O_CREAT | __O_TMPFILE)) ? (mode) : 0) +
Typo: (((flags) & (O_CREAT | __O_TMPFILE)) ? (mode) : 0)
+/** + * Arguments for how openat2(2) should open the target path. If @extra is zero, + * then openat2(2) is identical to openat(2). + * + * @flags: O_* flags (unknown flags ignored). + * @mode: O_CREAT file mode (ignored otherwise).
should probably say "O_CREAT/O_TMPFILE file mode".
+ * @upgrade_mask: restrict how the O_PATH may be re-opened (ignored otherwise).
+ * @resolve: RESOLVE_* flags (-EINVAL on unknown flags).
+ * @reserved: reserved for future extensions, must be zeroed.
+ */
+struct open_how {
+ __u32 flags;
+ union {
+ __u16 mode;
+ __u16 upgrade_mask;
+ };
+ __u16 resolve;So mode and upgrade_mask are naturally u16 aka mode_t. And yes, they probably never need to be used together, so the union works. That then makes the next member 2-byte aligned, so using a u16 for the resolve flags brings us to an 8-byte boundary, and 11 unused flag bits should be enough for a while. But it seems a bit artificial to cram all this together and then add 56 bytes of reserved space. Rasmus