/* * linux/fs/file.c * * Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes * * Manage the dynamic fd arrays in the process files_struct. */ #include <linux/module.h> #include <linux/fs.h> #include <linux/mm.h> #include <linux/time.h> #include <linux/sched.h> #include <linux/slab.h> #include <linux/vmalloc.h> #include <linux/file.h> #include <linux/fdtable.h> #include <linux/bitops.h> #include <linux/interrupt.h> #include <linux/spinlock.h> #include <linux/rcupdate.h> #include <linux/workqueue.h> struct fdtable_defer { spinlock_t lock; struct work_struct wq; struct fdtable *next; }; int sysctl_nr_open __read_mostly = 1024*1024; int sysctl_nr_open_min = BITS_PER_LONG; int sysctl_nr_open_max = 1024 * 1024; /* raised later */ /* * We use this list to defer free fdtables that have vmalloced * sets/arrays. By keeping a per-cpu list, we avoid having to embed * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in * this per-task structure. */ static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list); static inline void * alloc_fdmem(unsigned int size) { if (size <= PAGE_SIZE) return kmalloc(size, GFP_KERNEL); else return vmalloc(size); } static inline void free_fdarr(struct fdtable *fdt) { if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) kfree(fdt->fd); else vfree(fdt->fd); } static inline void free_fdset(struct fdtable *fdt) { if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2)) kfree(fdt->open_fds); else vfree(fdt->open_fds); } static void free_fdtable_work(struct work_struct *work) { struct fdtable_defer *f = container_of(work, struct fdtable_defer, wq); struct fdtable *fdt; spin_lock_bh(&f->lock); fdt = f->next; f->next = NULL; spin_unlock_bh(&f->lock); while(fdt) { struct fdtable *next = fdt->next; vfree(fdt->fd); free_fdset(fdt); kfree(fdt); fdt = next; } } void free_fdtable_rcu(struct rcu_head *rcu) { struct fdtable *fdt = container_of(rcu, struct fdtable, rcu); struct fdtable_defer *fddef; BUG_ON(!fdt); if (fdt->max_fds <= NR_OPEN_DEFAULT) { /* * This fdtable is embedded in the files structure and that * structure itself is getting destroyed. */ kmem_cache_free(files_cachep, container_of(fdt, struct files_struct, fdtab)); return; } if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) { kfree(fdt->fd); kfree(fdt->open_fds); kfree(fdt); } else { fddef = &get_cpu_var(fdtable_defer_list); spin_lock(&fddef->lock); fdt->next = fddef->next; fddef->next = fdt; /* vmallocs are handled from the workqueue context */ schedule_work(&fddef->wq); spin_unlock(&fddef->lock); put_cpu_var(fdtable_defer_list); } } /* * Expand the fdset in the files_struct. Called with the files spinlock * held for write. */ static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt) { unsigned int cpy, set; BUG_ON(nfdt->max_fds < ofdt->max_fds); cpy = ofdt->max_fds * sizeof(struct file *); set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *); memcpy(nfdt->fd, ofdt->fd, cpy); memset((char *)(nfdt->fd) + cpy, 0, set); cpy = ofdt->max_fds / BITS_PER_BYTE; set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE; memcpy(nfdt->open_fds, ofdt->open_fds, cpy); memset((char *)(nfdt->open_fds) + cpy, 0, set); memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy); memset((char *)(nfdt->close_on_exec) + cpy, 0, set); } static struct fdtable * alloc_fdtable(unsigned int nr) { struct fdtable *fdt; char *data; /* * Figure out how many fds we actually want to support in this fdtable. * Allocation steps are keyed to the size of the fdarray, since it * grows far faster than any of the other dynamic data. We try to fit * the fdarray into comfortable page-tuned chunks: starting at 1024B * and growing in powers of two from there on. */ nr /= (1024 / sizeof(struct file *)); nr = roundup_pow_of_two(nr + 1); nr *= (1024 / sizeof(struct file *)); /* * Note that this can drive nr *below* what we had passed if sysctl_nr_open * had been set lower between the check in expand_files() and here. Deal * with that in caller, it's cheaper that way. * * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise * bitmaps handling below becomes unpleasant, to put it mildly... */ if (unlikely(nr > sysctl_nr_open)) nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1; fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL); if (!fdt) goto out; fdt->max_fds = nr; data = alloc_fdmem(nr * sizeof(struct file *)); if (!data) goto out_fdt; fdt->fd = (struct file **)data; data = alloc_fdmem(max_t(unsigned int, 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES)); if (!data) goto out_arr; fdt->open_fds = (fd_set *)data; data += nr / BITS_PER_BYTE; fdt->close_on_exec = (fd_set *)data; INIT_RCU_HEAD(&fdt->rcu); fdt->next = NULL; return fdt; out_arr: free_fdarr(fdt); out_fdt: kfree(fdt); out: return NULL; } /* * Expand the file descriptor table. * This function will allocate a new fdtable and both fd array and fdset, of * the given size. * Return <0 error code on error; 1 on successful completion. * The files->file_lock should be held on entry, and will be held on exit. */ static int expand_fdtable(struct files_struct *files, int nr) __releases(files->file_lock) __acquires(files->file_lock) { struct fdtable *new_fdt, *cur_fdt; spin_unlock(&files->file_lock); new_fdt = alloc_fdtable(nr); spin_lock(&files->file_lock); if (!new_fdt) return -ENOMEM; /* * extremely unlikely race - sysctl_nr_open decreased between the check in * caller and alloc_fdtable(). Cheaper to catch it here... */ if (unlikely(new_fdt->max_fds <= nr)) { free_fdarr(new_fdt); free_fdset(new_fdt); kfree(new_fdt); return -EMFILE; } /* * Check again since another task may have expanded the fd table while * we dropped the lock */ cur_fdt = files_fdtable(files); if (nr >= cur_fdt->max_fds) { /* Continue as planned */ copy_fdtable(new_fdt, cur_fdt); rcu_assign_pointer(files->fdt, new_fdt); if (cur_fdt->max_fds > NR_OPEN_DEFAULT) free_fdtable(cur_fdt); } else { /* Somebody else expanded, so undo our attempt */ free_fdarr(new_fdt); free_fdset(new_fdt); kfree(new_fdt); } return 1; } /* * Expand files. * This function will expand the file structures, if the requested size exceeds * the current capacity and there is room for expansion. * Return <0 error code on error; 0 when nothing done; 1 when files were * expanded and execution may have blocked. * The files->file_lock should be held on entry, and will be held on exit. */ int expand_files(struct files_struct *files, int nr) { struct fdtable *fdt; fdt = files_fdtable(files); /* * N.B. For clone tasks sharing a files structure, this test * will limit the total number of files that can be opened. */ if (nr >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur) return -EMFILE; /* Do we need to expand? */ if (nr < fdt->max_fds) return 0; /* Can we expand? */ if (nr >= sysctl_nr_open) return -EMFILE; /* All good, so we try */ return expand_fdtable(files, nr); } static int count_open_files(struct fdtable *fdt) { int size = fdt->max_fds; int i; /* Find the last open fd */ for (i = size/(8*sizeof(long)); i > 0; ) { if (fdt->open_fds->fds_bits[--i]) break; } i = (i+1) * 8 * sizeof(long); return i; } /* * Allocate a new files structure and copy contents from the * passed in files structure. * errorp will be valid only when the returned files_struct is NULL. */ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp) { struct files_struct *newf; struct file **old_fds, **new_fds; int open_files, size, i; struct fdtable *old_fdt, *new_fdt; *errorp = -ENOMEM; newf = kmem_cache_alloc(files_cachep, GFP_KERNEL); if (!newf) goto out; atomic_set(&newf->count, 1); spin_lock_init(&newf->file_lock); newf->next_fd = 0; new_fdt = &newf->fdtab; new_fdt->max_fds = NR_OPEN_DEFAULT; new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init; new_fdt->open_fds = (fd_set *)&newf->open_fds_init; new_fdt->fd = &newf->fd_array[0]; INIT_RCU_HEAD(&new_fdt->rcu); new_fdt->next = NULL; spin_lock(&oldf->file_lock); old_fdt = files_fdtable(oldf); open_files = count_open_files(old_fdt); /* * Check whether we need to allocate a larger fd array and fd set. */ while (unlikely(open_files > new_fdt->max_fds)) { spin_unlock(&oldf->file_lock); if (new_fdt != &newf->fdtab) { free_fdarr(new_fdt); free_fdset(new_fdt); kfree(new_fdt); } new_fdt = alloc_fdtable(open_files - 1); if (!new_fdt) { *errorp = -ENOMEM; goto out_release; } /* beyond sysctl_nr_open; nothing to do */ if (unlikely(new_fdt->max_fds < open_files)) { free_fdarr(new_fdt); free_fdset(new_fdt); kfree(new_fdt); *errorp = -EMFILE; goto out_release; } /* * Reacquire the oldf lock and a pointer to its fd table * who knows it may have a new bigger fd table. We need * the latest pointer. */ spin_lock(&oldf->file_lock); old_fdt = files_fdtable(oldf); open_files = count_open_files(old_fdt); } old_fds = old_fdt->fd; new_fds = new_fdt->fd; memcpy(new_fdt->open_fds->fds_bits, old_fdt->open_fds->fds_bits, open_files/8); memcpy(new_fdt->close_on_exec->fds_bits, old_fdt->close_on_exec->fds_bits, open_files/8); for (i = open_files; i != 0; i--) { struct file *f = *old_fds++; if (f) { get_file(f); } else { /* * The fd may be claimed in the fd bitmap but not yet * instantiated in the files array if a sibling thread * is partway through open(). So make sure that this * fd is available to the new process. */ FD_CLR(open_files - i, new_fdt->open_fds); } rcu_assign_pointer(*new_fds++, f); } spin_unlock(&oldf->file_lock); /* compute the remainder to be cleared */ size = (new_fdt->max_fds - open_files) * sizeof(struct file *); /* This is long word aligned thus could use a optimized version */ memset(new_fds, 0, size); if (new_fdt->max_fds > open_files) { int left = (new_fdt->max_fds-open_files)/8; int start = open_files / (8 * sizeof(unsigned long)); memset(&new_fdt->open_fds->fds_bits[start], 0, left); memset(&new_fdt->close_on_exec->fds_bits[start], 0, left); } rcu_assign_pointer(newf->fdt, new_fdt); return newf; out_release: kmem_cache_free(files_cachep, newf); out: return NULL; } static void __devinit fdtable_defer_list_init(int cpu) { struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu); spin_lock_init(&fddef->lock); INIT_WORK(&fddef->wq, free_fdtable_work); fddef->next = NULL; } void __init files_defer_init(void) { int i; for_each_possible_cpu(i) fdtable_defer_list_init(i); sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG; } struct files_struct init_files = { .count = ATOMIC_INIT(1), .fdt = &init_files.fdtab, .fdtab = { .max_fds = NR_OPEN_DEFAULT, .fd = &init_files.fd_array[0], .close_on_exec = (fd_set *)&init_files.close_on_exec_init, .open_fds = (fd_set *)&init_files.open_fds_init, .rcu = RCU_HEAD_INIT, }, .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock), }; /* * allocate a file descriptor, mark it busy. */ int alloc_fd(unsigned start, unsigned flags) { struct files_struct *files = current->files; unsigned int fd; int error; struct fdtable *fdt; spin_lock(&files->file_lock); repeat: fdt = files_fdtable(files); fd = start; if (fd < files->next_fd) fd = files->next_fd; if (fd < fdt->max_fds) fd = find_next_zero_bit(fdt->open_fds->fds_bits, fdt->max_fds, fd); error = expand_files(files, fd); if (error < 0) goto out; /* * If we needed to expand the fs array we * might have blocked - try again. */ if (error) goto repeat; if (start <= files->next_fd) files->next_fd = fd + 1; FD_SET(fd, fdt->open_fds); if (flags & O_CLOEXEC) FD_SET(fd, fdt->close_on_exec); else FD_CLR(fd, fdt->close_on_exec); error = fd; #if 1 /* Sanity check */ if (rcu_dereference_raw(fdt->fd[fd]) != NULL) { printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd); rcu_assign_pointer(fdt->fd[fd], NULL); } #endif out: spin_unlock(&files->file_lock); return error; } int get_unused_fd(void) { return alloc_fd(0, 0); } EXPORT_SYMBOL(get_unused_fd);