Date: Thu, 15 Aug 2019 23:21:41 +0000 (UTC) From: Rick Macklem <rmacklem@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r351106 - head/sys/kern Message-ID: <201908152321.x7FNLfQW055908@repo.freebsd.org>
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Author: rmacklem Date: Thu Aug 15 23:21:41 2019 New Revision: 351106 URL: https://svnweb.freebsd.org/changeset/base/351106 Log: Fix copy_file_range(2) so that unneeded blocks are not allocated to the output file. When the byte range for copy_file_range(2) doesn't go to EOF on the output file and there is a hole in the input file, a hole must be "punched" in the output file. This is done by writing a block of bytes all set to 0. Without this patch, the write is done unconditionally which means that, if the output file already has a hole in that byte range, a unneeded data block of all 0 bytes would be allocated. This patch adds code to check for a hole in the output file, so that it can skip doing the write if there is already a hole in that byte range of the output file. This avoids unnecessary allocation of blocks to the output file. Reviewed by: kib Differential Revision: https://reviews.freebsd.org/D21155 Modified: head/sys/kern/vfs_vnops.c Modified: head/sys/kern/vfs_vnops.c ============================================================================== --- head/sys/kern/vfs_vnops.c Thu Aug 15 22:55:59 2019 (r351105) +++ head/sys/kern/vfs_vnops.c Thu Aug 15 23:21:41 2019 (r351106) @@ -2713,18 +2713,92 @@ mem_iszero(void *dat, int len) } /* + * Look for a hole in the output file and, if found, adjust *outoffp + * and *xferp to skip past the hole. + * *xferp is the entire hole length to be written and xfer2 is how many bytes + * to be written as 0's upon return. + */ +static off_t +vn_skip_hole(struct vnode *outvp, off_t xfer2, off_t *outoffp, off_t *xferp, + off_t *dataoffp, off_t *holeoffp, struct ucred *cred) +{ + int error; + off_t delta; + + if (*holeoffp == 0 || *holeoffp <= *outoffp) { + *dataoffp = *outoffp; + error = VOP_IOCTL(outvp, FIOSEEKDATA, dataoffp, 0, cred, + curthread); + if (error == 0) { + *holeoffp = *dataoffp; + error = VOP_IOCTL(outvp, FIOSEEKHOLE, holeoffp, 0, cred, + curthread); + } + if (error != 0 || *holeoffp == *dataoffp) { + /* + * Since outvp is unlocked, it may be possible for + * another thread to do a truncate(), lseek(), write() + * creating a hole at startoff between the above + * VOP_IOCTL() calls, if the other thread does not do + * rangelocking. + * If that happens, *holeoffp == *dataoffp and finding + * the hole has failed, so disable vn_skip_hole(). + */ + *holeoffp = -1; /* Disable use of vn_skip_hole(). */ + return (xfer2); + } + KASSERT(*dataoffp >= *outoffp, + ("vn_skip_hole: dataoff=%jd < outoff=%jd", + (intmax_t)*dataoffp, (intmax_t)*outoffp)); + KASSERT(*holeoffp > *dataoffp, + ("vn_skip_hole: holeoff=%jd <= dataoff=%jd", + (intmax_t)*holeoffp, (intmax_t)*dataoffp)); + } + + /* + * If there is a hole before the data starts, advance *outoffp and + * *xferp past the hole. + */ + if (*dataoffp > *outoffp) { + delta = *dataoffp - *outoffp; + if (delta >= *xferp) { + /* Entire *xferp is a hole. */ + *outoffp += *xferp; + *xferp = 0; + return (0); + } + *xferp -= delta; + *outoffp += delta; + xfer2 = MIN(xfer2, *xferp); + } + + /* + * If a hole starts before the end of this xfer2, reduce this xfer2 so + * that the write ends at the start of the hole. + * *holeoffp should always be greater than *outoffp, but for the + * non-INVARIANTS case, check this to make sure xfer2 remains a sane + * value. + */ + if (*holeoffp > *outoffp && *holeoffp < *outoffp + xfer2) + xfer2 = *holeoffp - *outoffp; + return (xfer2); +} + +/* * Write an xfer sized chunk to outvp in blksize blocks from dat. * dat is a maximum of blksize in length and can be written repeatedly in * the chunk. * If growfile == true, just grow the file via vn_truncate_locked() instead * of doing actual writes. + * If checkhole == true, a hole is being punched, so skip over any hole + * already in the output file. */ static int vn_write_outvp(struct vnode *outvp, char *dat, off_t outoff, off_t xfer, - u_long blksize, bool growfile, struct ucred *cred) + u_long blksize, bool growfile, bool checkhole, struct ucred *cred) { struct mount *mp; - off_t xfer2; + off_t dataoff, holeoff, xfer2; int error, lckf; /* @@ -2733,7 +2807,24 @@ vn_write_outvp(struct vnode *outvp, char *dat, off_t o * done for each iteration, since the xfer argument can be very * large if there is a large hole to punch in the output file. */ + error = 0; + holeoff = 0; do { + xfer2 = MIN(xfer, blksize); + if (checkhole) { + /* + * Punching a hole. Skip writing if there is + * already a hole in the output file. + */ + xfer2 = vn_skip_hole(outvp, xfer2, &outoff, &xfer, + &dataoff, &holeoff, cred); + if (xfer == 0) + break; + if (holeoff < 0) + checkhole = false; + KASSERT(xfer2 > 0, ("vn_write_outvp: xfer2=%jd", + (intmax_t)xfer2)); + } bwillwrite(); mp = NULL; error = vn_start_write(outvp, &mp, V_WAIT); @@ -2749,7 +2840,6 @@ vn_write_outvp(struct vnode *outvp, char *dat, off_t o error = vn_truncate_locked(outvp, outoff + xfer, false, cred); else { - xfer2 = MIN(xfer, blksize); error = vn_rdwr(UIO_WRITE, outvp, dat, xfer2, outoff, UIO_SYSSPACE, IO_NODELOCKED, curthread->td_ucred, cred, NULL, curthread); @@ -2916,7 +3006,7 @@ vn_generic_copy_file_range(struct vnode *invp, off_t * memset(dat, 0, MIN(xfer2, blksize)); error = vn_write_outvp(outvp, dat, *outoffp, xfer2, blksize, false, - outcred); + holeout > 0, outcred); } if (error == 0 && *outoffp + xfer > @@ -2924,7 +3014,7 @@ vn_generic_copy_file_range(struct vnode *invp, off_t * /* Grow last block. */ error = vn_write_outvp(outvp, dat, *outoffp, xfer, blksize, true, - outcred); + false, outcred); if (error == 0) { *inoffp += xfer; *outoffp += xfer; @@ -2980,7 +3070,8 @@ vn_generic_copy_file_range(struct vnode *invp, off_t * error = vn_write_outvp(outvp, dat, *outoffp, xfer, blksize, readzeros && xfer == len && - *outoffp >= va.va_size, outcred); + *outoffp >= va.va_size, false, + outcred); if (error == 0) { *inoffp += xfer; startoff += xfer;
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