Get empty filp

http://lxr.free-electrons.com/source/fs/file_table.c#L104

94 /* Find an unused file structure and return a pointer to it.
95  * Returns an error pointer if some error happend e.g. we over file
96  * structures limit, run out of memory or operation is not permitted.
97  *
98  * Be very careful using this.  You are responsible for
99  * getting write access to any mount that you might assign

100 * to this filp, if it is opened for write. If this is not 101 * done, you will imbalance int the mount's writer count 102 * and a warning at __fput() time. 103 */ 104 struct file *get_empty_filp(void) 105 { 106 const struct cred *cred = current_cred(); 107 static long old_max; 108 struct file *f; 109 int error; 110 111 /* 112 * Privileged users can go above max_files 113 */ 114 if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { 115 /* 116 * percpu_counters are inaccurate. Do an expensive check before 117 * we go and fail. 118 */ 119 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files) 120 goto over; 121 } 122 123 f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); 124 if (unlikely(!f)) 125 return ERR_PTR(-ENOMEM); 126 127 percpu_counter_inc(&nr_files); 128 f->f_cred = get_cred(cred); 129 error = security_file_alloc(f); 130 if (unlikely(error)) { 131 file_free(f); 132 return ERR_PTR(error); 133 } 134 135 atomic_long_set(&f->f_count, 1); 136 rwlock_init(&f->f_owner.lock); 137 spin_lock_init(&f->f_lock); 138 mutex_init(&f->f_pos_lock); 139 eventpoll_init_file(f); 140 /* f->f_version: 0 */ 141 return f; 142 143 over: 144 /* Ran out of filps - report that */ 145 if (get_nr_files() > old_max) { 146 pr_info("VFS: file-max limit %lu reached\n", get_max_files()); 147 old_max = get_nr_files(); 148 } 149 return ERR_PTR(-ENFILE); 150 }