X-Git-Url: https://git.camperquake.de/gitweb.cgi?a=blobdiff_plain;f=module%2Fzfs%2Fzpl_file.c;h=ed6704bb2066de46b93b644bd790887651d4e035;hb=4c0d8e50b99b4f3b4a9b7bc67ac7fc4e406f5755;hp=41901bb6caf8747da0d8a472d5353666dadacfec;hpb=1efb473f8919c5f195e127136b79c6d3b1eb1c81;p=zfs.git diff --git a/module/zfs/zpl_file.c b/module/zfs/zpl_file.c index 41901bb..ed6704b 100644 --- a/module/zfs/zpl_file.c +++ b/module/zfs/zpl_file.c @@ -45,8 +45,7 @@ zpl_readdir(struct file *filp, void *dirent, filldir_t filldir) return (error); } -static int -zpl_fsync(struct file *filp, struct dentry *dentry, int datasync) +ZPL_FSYNC_PROTO(zpl_fsync, filp, unused_dentry, datasync) { cred_t *cr; int error; @@ -145,24 +144,185 @@ zpl_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos) return (wrote); } +/* + * It's worth taking a moment to describe how mmap is implemented + * for zfs because it differs considerably from other Linux filesystems. + * However, this issue is handled the same way under OpenSolaris. + * + * The issue is that by design zfs bypasses the Linux page cache and + * leaves all caching up to the ARC. This has been shown to work + * well for the common read(2)/write(2) case. However, mmap(2) + * is problem because it relies on being tightly integrated with the + * page cache. To handle this we cache mmap'ed files twice, once in + * the ARC and a second time in the page cache. The code is careful + * to keep both copies synchronized. + * + * When a file with an mmap'ed region is written to using write(2) + * both the data in the ARC and existing pages in the page cache + * are updated. For a read(2) data will be read first from the page + * cache then the ARC if needed. Neither a write(2) or read(2) will + * will ever result in new pages being added to the page cache. + * + * New pages are added to the page cache only via .readpage() which + * is called when the vfs needs to read a page off disk to back the + * virtual memory region. These pages may be modified without + * notifying the ARC and will be written out periodically via + * .writepage(). This will occur due to either a sync or the usual + * page aging behavior. Note because a read(2) of a mmap'ed file + * will always check the page cache first even when the ARC is out + * of date correct data will still be returned. + * + * While this implementation ensures correct behavior it does have + * have some drawbacks. The most obvious of which is that it + * increases the required memory footprint when access mmap'ed + * files. It also adds additional complexity to the code keeping + * both caches synchronized. + * + * Longer term it may be possible to cleanly resolve this wart by + * mapping page cache pages directly on to the ARC buffers. The + * Linux address space operations are flexible enough to allow + * selection of which pages back a particular index. The trick + * would be working out the details of which subsystem is in + * charge, the ARC, the page cache, or both. It may also prove + * helpful to move the ARC buffers to a scatter-gather lists + * rather than a vmalloc'ed region. + */ +static int +zpl_mmap(struct file *filp, struct vm_area_struct *vma) +{ + znode_t *zp = ITOZ(filp->f_mapping->host); + int error; + + error = generic_file_mmap(filp, vma); + if (error) + return (error); + + mutex_enter(&zp->z_lock); + zp->z_is_mapped = 1; + mutex_exit(&zp->z_lock); + + return (error); +} + +/* + * Populate a page with data for the Linux page cache. This function is + * only used to support mmap(2). There will be an identical copy of the + * data in the ARC which is kept up to date via .write() and .writepage(). + * + * Current this function relies on zpl_read_common() and the O_DIRECT + * flag to read in a page. This works but the more correct way is to + * update zfs_fillpage() to be Linux friendly and use that interface. + */ +static int +zpl_readpage(struct file *filp, struct page *pp) +{ + struct inode *ip; + loff_t off, i_size; + size_t len, wrote; + cred_t *cr; + void *pb; + int error = 0; + + ASSERT(PageLocked(pp)); + ip = pp->mapping->host; + off = page_offset(pp); + i_size = i_size_read(ip); + ASSERT3S(off, <, i_size); + + cr = (cred_t *)get_current_cred(); + len = MIN(PAGE_CACHE_SIZE, i_size - off); + + pb = kmap(pp); + + /* O_DIRECT is passed to bypass the page cache and avoid deadlock. */ + wrote = zpl_read_common(ip, pb, len, off, UIO_SYSSPACE, O_DIRECT, cr); + if (wrote != len) + error = -EIO; + + if (!error && (len < PAGE_CACHE_SIZE)) + memset(pb + len, 0, PAGE_CACHE_SIZE - len); + + kunmap(pp); + put_cred(cr); + + if (error) { + SetPageError(pp); + ClearPageUptodate(pp); + } else { + ClearPageError(pp); + SetPageUptodate(pp); + flush_dcache_page(pp); + } + + unlock_page(pp); + + return (error); +} + +/* + * Write out dirty pages to the ARC, this function is only required to + * support mmap(2). Mapped pages may be dirtied by memory operations + * which never call .write(). These dirty pages are kept in sync with + * the ARC buffers via this hook. + * + * Currently this function relies on zpl_write_common() and the O_DIRECT + * flag to push out the page. This works but the more correct way is + * to update zfs_putapage() to be Linux friendly and use that interface. + */ +static int +zpl_writepage(struct page *pp, struct writeback_control *wbc) +{ + struct inode *ip; + loff_t off, i_size; + size_t len, read; + cred_t *cr; + void *pb; + int error = 0; + + ASSERT(PageLocked(pp)); + ip = pp->mapping->host; + off = page_offset(pp); + i_size = i_size_read(ip); + + cr = (cred_t *)get_current_cred(); + len = MIN(PAGE_CACHE_SIZE, i_size - off); + + pb = kmap(pp); + + /* O_DIRECT is passed to bypass the page cache and avoid deadlock. */ + read = zpl_write_common(ip, pb, len, off, UIO_SYSSPACE, O_DIRECT, cr); + if (read != len) + error = -EIO; + + kunmap(pp); + put_cred(cr); + + if (error) { + SetPageError(pp); + ClearPageUptodate(pp); + } else { + ClearPageError(pp); + SetPageUptodate(pp); + } + + unlock_page(pp); + + return (error); +} + const struct address_space_operations zpl_address_space_operations = { -#if 0 .readpage = zpl_readpage, .writepage = zpl_writepage, - .direct_IO = zpl_direct_IO, -#endif }; const struct file_operations zpl_file_operations = { .open = generic_file_open, .llseek = generic_file_llseek, - .read = zpl_read, /* do_sync_read */ - .write = zpl_write, /* do_sync_write */ + .read = zpl_read, + .write = zpl_write, .readdir = zpl_readdir, - .mmap = generic_file_mmap, + .mmap = zpl_mmap, .fsync = zpl_fsync, - .aio_read = NULL, /* generic_file_aio_read */ - .aio_write = NULL, /* generic_file_aio_write */ }; const struct file_operations zpl_dir_file_operations = {