diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/atomic.h | 26 | ||||
| -rw-r--r-- | include/linux/fs.h | 29 |
2 files changed, 52 insertions, 3 deletions
diff --git a/include/linux/atomic.h b/include/linux/atomic.h index ee456c79b0e6..bc6615d4132b 100644 --- a/include/linux/atomic.h +++ b/include/linux/atomic.h @@ -34,6 +34,32 @@ static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint) } #endif +#ifndef atomic_inc_unless_negative +static inline int atomic_inc_unless_negative(atomic_t *p) +{ + int v, v1; + for (v = 0; v >= 0; v = v1) { + v1 = atomic_cmpxchg(p, v, v + 1); + if (likely(v1 == v)) + return 1; + } + return 0; +} +#endif + +#ifndef atomic_dec_unless_positive +static inline int atomic_dec_unless_positive(atomic_t *p) +{ + int v, v1; + for (v = 0; v <= 0; v = v1) { + v1 = atomic_cmpxchg(p, v, v - 1); + if (likely(v1 == v)) + return 1; + } + return 0; +} +#endif + #ifndef CONFIG_ARCH_HAS_ATOMIC_OR static inline void atomic_or(int i, atomic_t *v) { diff --git a/include/linux/fs.h b/include/linux/fs.h index d04e55586a17..8c84ed930389 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -392,8 +392,8 @@ struct inodes_stat_t { #include <linux/semaphore.h> #include <linux/fiemap.h> #include <linux/rculist_bl.h> +#include <linux/atomic.h> -#include <asm/atomic.h> #include <asm/byteorder.h> struct export_operations; @@ -2195,8 +2195,31 @@ static inline bool execute_ok(struct inode *inode) return (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode); } -extern int get_write_access(struct inode *); -extern int deny_write_access(struct file *); +/* + * get_write_access() gets write permission for a file. + * put_write_access() releases this write permission. + * This is used for regular files. + * We cannot support write (and maybe mmap read-write shared) accesses and + * MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode + * can have the following values: + * 0: no writers, no VM_DENYWRITE mappings + * < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist + * > 0: (i_writecount) users are writing to the file. + * + * Normally we operate on that counter with atomic_{inc,dec} and it's safe + * except for the cases where we don't hold i_writecount yet. Then we need to + * use {get,deny}_write_access() - these functions check the sign and refuse + * to do the change if sign is wrong. + */ +static inline int get_write_access(struct inode *inode) +{ + return atomic_inc_unless_negative(&inode->i_writecount) ? 0 : -ETXTBSY; +} +static inline int deny_write_access(struct file *file) +{ + struct inode *inode = file->f_path.dentry->d_inode; + return atomic_dec_unless_positive(&inode->i_writecount) ? 0 : -ETXTBSY; +} static inline void put_write_access(struct inode * inode) { atomic_dec(&inode->i_writecount); |